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2015 Fall

Nanomaterials,Nanostructures and Nano devices


Molecular Materials for Quantum Computing

Quantum computing will lead the future revolution of information technology. Current efforts in materials science focus on the physical realization of qubits and qugates. This symposium will highlight the contribution to this from the molecular materials’ perspective, mainly on the manipulation of the electronic spin as the basic unit of quantum information.




Quantum information processing proposes to exploit the laws of quantum mechanics for the realization of logic operations and implementation of algorithms. The realization of Quantum Computing will outperform current classic information technology by dramatically increasing speed and providing the capacity to handle intractable problems, like the simulation of quantum systems. Current efforts focus on the physical realization of the hardware to implement these principles and very promising candidates have arisen from the materials science arena. One promising approach is encoding the qubit information in the quantum states of the electronic spin contained in molecular materials. Indeed the spin carried by molecular species has been shown to exhibit sufficiently high quantum coherence times for the realization of quantum operations and algorithms. Theoretical and empirical methods have been developed in order to predict and enhance this property, most especially in lanthanide-based qubits. The versatility of chemistry is proving highly beneficial for the design and tuning of scalable architectures able to bring about complex operations. Several proposal and prototypes of multi-qubit quantum gates have been already put forward, specifically for CNOT and SWAP operations. Current efforts focus on integrating small ensembles, or even single molecules on suitable substrates for their manipulation. These very exciting developments give great promise to this proposition. These have been possible thanks to the interdisciplinary efforts of chemists, spectroscopists, physicists and theoreticians. The symposium aims at bringing together for the first time the main actors of this very recent and rapidly growing area, as an idea to stimulate further development in this promising avenue. The speakers that have confirmed their participation belong to the various areas of expertise that have made possible these developments with their seminal publications. In addition, a prominent scholar has accepted to participate, who has recently contributed decisively, from a field other than molecular materials, to develop the goal of using spin qubits. This with the aim of visualizing the broadness of the subject.


Hot topics to be covered by the symposium (but is not limited)


  • Chemical design of qubits using lanthanide and transition metal complexes
  • Organic radicals for quantum computing
  • Design and control of quantum coherence through chemistry
  • Physical methods to unveil and study quantum entanglement within molecules
  • Realization of multi-qubit quantum gates
  • Pulsed and HF-EPR for the detection and characterization of quantum coherence
  • Simulation of magnetic anisotropy and quantum coherence through theoretical methods
  • Quantum simulation of quantum systems
  • Quantum Manipulation of small molecular or atomic ensembles
  • Surface nanostructuration of molecular qubits and qugates


Confirmed list of invited speakers


  • Alejandro Gaita Ariño (University of Valencia, Spain) –"Rational design of coherent molecular spin qubits"
  • Takeji Takui (Osaka City University, Japan) –"Milestones to molecular spin quantum computers
  • Joris van Slageren (University of Stuttgart, Germany) –“Quantum Coherence in Metal Dithiolates”
  • Steven Hill (National High Magnetic Field Laboratory, USA) –“Atomic Clock Transitions in Lanthanide Molecular Qubits”
  • Mario Ruben (Karlsruhe Institute of Technology, Germany) –“Molecular Quantum Spintronics”
  • Andrea Morello (University of New South Wales, Australia) –“Quantum computing with spins: atoms and molecules”
  • Filippo Troiani (CNR Modena, Italy)
  • Paolo Santini (U. Parma, Italy)


Confirmed list of scientific committee members


  • Fernando LUIS (Spain)
  • Daniel Loss (Switzerland)
  • Arzhang Ardavan (UK)
  • Stefano Carretta (Italy)
  • Enrique del Barco (USA)
  • Eugenio Coronado (Spain)

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09:00 Welcome/Introduction    
Session 1 : Guillem Aromí
Authors : J. van Slageren, K. Bader, D. Dengler, S. Lenz, B. Endeward, P. Neugebauer
Affiliations : University of Stuttgart; University of Stuttgart; University of Stuttgart; University of Stuttgart; Centre for Biomolecular Magnetic Resonance Goethe University Frankfurt; University of Stuttgart;

Resume : Molecular nanomagnets have been proposed as prime quantum bit candidates. Quantum computing promises to enable calculations that will forever remain intractable with conventional computers. In principle, any two-level system will function as a qubit. One of the decisive quantities which determine the usefulness of a particular system is the ratio of the quantum coherence time and the time needed for a single quantum operation. The latter is given by electronics constraints, thus only the former can be optimized by chemical means. The quantum coherence time is the lifetime of an arbitrary superposition state, and corresponds to the time available for the quantum computation. The advantage of molecular systems is that their properties may be tuned continuously and almost without limitations by chemical synthetic means. This feature is especially useful, given the fact that quantum computing only becomes competitive if networks of hundreds of interacting qubits can be generated. In that respect, the fact that molecules have been shown the ability to form long-range ordered arrays on surfaces is also beneficial. However, thus far, quantum coherence times have been less than astounding, with the current record 15 μs at 1.5 K. We have recently shown that single ion systems (i.e., mononuclear complexes) can display much longer coherence time. Thus, we have found coherence times of up to 68 μs at 7 K for (PPh4-d20)2[Cu(mnt)2] and even at room temperature, the quantum coherence time is almost a microsecond.[1] Thus, the quantum coherence time exceeds that of prime competitors, such as diamond NV centres and phosphorus dopants in silicon in certain conditions. In this presentation, we will show published results,[1 – 4] as well as new results on single-qubit systems, two-qubit systems and on triangular qubits featuring antisymmetric exchange interactions. The last of these were predicted to be addressable by means of microwave electric fields, which would enable local control. [1] K. Bader, D. Dengler, S. Lenz, B. Endeward, S.D. Jiang, P. Neugebauer, J. van Slageren, Nat. Commun., 5, 5304 (2014); [2] P. Lutz, R. Marx, D. Dengler, A. Kromer, J. van Slageren, Mol. Phys., 111, 2897 – 2902 (2013); [3] C. Schlegel, J. van Slageren, G. Timco, R.E.P. Winpenny, M. Dressel, Phys. Rev. B, 83, 134407 (2011); [4] C. Schlegel, J. van Slageren, M. Manoli, E.K. Brechin, M. Dressel, Phys. Rev. Lett., 101, 147203 (2008)

Authors : Arzhang Ardavan (1), Alice M. Bowen (1), Antonio Fernandez (2), Alistair J. Fielding (2), Danielle Kaminski (1), Fabrizio Moro (2), Christopher A. Muryn (2), Matthew D. Wise (3), Albert Ruggi (3), Eric J.L. McInnes (2), Kay Severin (3), Grigore A. Timco (2), Christiane R. Timmel (4), Floriana Tuna (2), George F.S. Whitehead (2), Richard E. P. Winpenny (2)
Affiliations : 1. Centre for Advanced Electron Spin Resonance, The Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, U.K. 2. School of Chemistry & Photon Science Institute, The University of Manchester, Oxford Road, Manchester, M13 9PL, U.K. 3. Institut des Sciences et Ingenierie Chimiques, Ecole Polytechnique Federale de Lausanne (EPFL), 1015 Lausanne, Switzerland. 4. Centre for Advanced Electron Spin Resonance, Inorganic Chemistry Laboratory, South Parks Road, University of Oxford, OX1 3QR, U.K.

Resume : Proposals for systems embodying condensed matter spin qubits cover a very wide range of length scales, from atomic defects in semiconductors all the way to micron-sized lithographically-defined structures. Intermediate scale molecular components exhibit advantages of both limits: like atomic defects, large numbers of identical components can be fabricated; as for lithographically-defined structures, each component can be tailored to optimize properties such as quantum coherence. We have demonstrated what is perhaps the most potent advantage of molecular spin qubits, the scalability of quantum information processing structures using bottom-up chemical self-assembly. Using Cr7Ni spin qubit building blocks, we have constructed several families of two-qubit molecular structures with a range of linking strategies. For each family, long coherence times are preserved, and we demonstrate control over the inter-qubit quantum interactions that can be used to mediate two-qubit quantum gates.

Authors : Jakub Łuczak, Bogdan R. Bułka
Affiliations : Institute of Molecular Physics PAS, M. Smoluchowskiego 17, 60-179 Poznań, Poland

Resume : Motivated by recent experiments [1] we undertaken theoretical studies on spin qubits encoded in an artificial triangular molecule built on three coherently coupled quantum dots [2]. The qubit operates in the doublet subspace due to DiVincenzo et al. [3] scheme. The fast qubit operations can be done purely electrically, moreover the doublet subspace is immunity to decoherence processes [4]. In calculations we use the Heisenberg Hamiltonian with the exchange interaction controlled by potentials applied to local electrodes which change the triangular symmetry. This effect affects the doublets, and therefore, it can be used to encode the qubit in the state |0> and |1> as well as to perform one qubit operations. We present a new method to read-out the qubit states based on a doublet blockade effect observed in transport. For some symmetry the current is blocked due to asymmetry of tunnel rates between the doublets and the electrodes. Dynamics of the system in the limit of the doublet blockade is studied as well. Finally two interacting qubits are considered for different connections and symmetries of the qubits. We show how to perform two-qubit logical gates using only in few control impulses. This work has been supported by NCN under the contract DEC-2012/05/B/ST3/03208 [1] see e.g. L. Gaudreau, et al., Nature Phys. 8, 54, (2012). [2] J. Łuczak et al. PRB 90, 165427, (2014). [3] D. P. DiVincenzo et al., Nature 408, 339, (2000). [4] D. A. Lidar et al. PRL 81, 2594 (1998)

10:30 Coffee Break    
Session 2 : Joris van Slageren
Authors : Andrea Morello
Affiliations : Centre for Quantum Computation and Communication Technology, UNSW Australia, Sydney, Australia

Resume : A phosphorus (31P) donor in silicon is, almost literally, the equivalent of a hydrogen atom in vacuum. It possesses electron and nuclear spins 1/2 which act as natural qubits, and the host material can be isotopically purified to be almost perfectly free of other spin species, ensuring extraordinary coherence times. I will present the current state-of-the-art in silicon quantum information technologies. Both the electron and the nuclear spin of a single 31P atom can be read out in single-shot with high fidelity, through a nanoelectronic device compatible with standard semiconductor fabrication. High-frequency microwave pulses can be used to prepare arbitrary quantum states of the spin qubits, with fidelity in excess of 99%. Our latest experiment on the 31P nucleus has established the record coherence time (35 seconds) for any single qubit in solid state, by making use of an isotopically enriched 28Si epilayer. To scale up the system to multi-qubit quantum logic operations, we need to engineer the coupling between multiple atoms, akin to creating artificial molecules within the silicon crystal. We have observed the singlet/triplet states of a strongly-coupled donor pair, proposed a new scheme for entangling two-qubit logic gates that does not require atomically precise placement of the 31P donors, and we are exploring cavity-mediated long-distance spin coupling. These results show that silicon can be successfully adapted to host quantum information hardware.

Authors : Alasdair Formanuik, Ana Maria Ariciu, Eric McInnes, David Mills, Floriana Tuna*
Affiliations : School of Chemistry and Photon Science Institute, University of Manchester

Resume : There is significant current interest in the development of molecular spin qubits whose properties are suitable for the implementation of logic operations and algorithms. This has led to the discovery of very interesting systems with long qubit phase memory times, Tm. Although metal complexes proved to be very promising candidates for QIP, focus has been placed so far on transition and lanthanide complexes only. Here we show for the first time that organometallic actinide complexes are ideal systems to provide molecular spin qubits with very long coherence times, which could be detected and characterized by pulsed EPR methods (ESSEM, HYSCORE, ENDOR) at temperatures as high as 150 K. The main focus of this lecture will be on organometallic Th(III) and U(III) complexes, with a special emphasis on EPR characterization.

Authors : Jorge Salinas Uber (a), Marta Estrader (a), D. Dengler (b), Olivier Roubeau (c), J. van Slageren (b) and Guillem Aromí (a)
Affiliations : (a) Departament de Química Inorgànica, Universitat de Barcelona, Barcelona, Spain; (b) Institut für Physikalische Chemie, Universität Stuttgart, Stuttgart, Germany. (c) Instituto de Ciencia de Materiales de Aragón (ICMA), CSIC and Universidad de Zaragoza, Zaragoza, Spain

Resume : A fascinating goal in coordination chemistry is to manipulate photochemically magnetic properties of complexes, which could find applications in important areas such as that of spin-based quantum computing. Indeed, molecules exhibiting well defined spins separated by a photoswitchable moiety could serve as prototypes of a SWAP quantum gate if the interaction between both spins can be controlled by light irradiation in a similar way as proposed for an electrically controlled spin-based gate. Following the previous idea, we have designed and synthesized a new ligand to assemble pure weakly coupled pairs of heterometallic dimers of the type [MM’•••M’M] (M,M’= Cu, Ni, Zn, Co) through site-selective control of different spin carrier metals in a single molecule. We have measured by pulsed EPR techniques the quantum coherence of the spin transitions within each dimer of some of these molecules. In addition, the ligand possesses a photochromic unit able to switch the quantum correlation between both total spins through light. Photocyclization is carried out using UV light and reversed with visible light. We present the structural, magnetic and optical properties of this new family of compounds and evaluate their potential as prototypes of SWAP quantum gates.

Authors : A. Ghirri^1,C. Bonizzoni^2 D. Gerace^3, S. Sanna^3, A. Cassinese^4, M. Affronte^2
Affiliations : 1^Istituto Nanoscienze - CNR, Centro S3, via Campi 213/a, 41125 Modena, Italy 2^Dipartimento Fisica, Informatica e Matematica, Universita di Modena e Reggio Emilia and Istituto Nanoscienze - CNR, Centro S3, via Campi 213/a, 41125 Modena, Italy 3^Dipartimento di Fisica, Universita di Pavia, via Bassi 6, 27100 Pavia, Italy 4^CNR-SPIN and Dipartimento di Fisica, Universita􏱃 di Napoli Federico II, 80138 Napoli, Italy

Resume : We report recent experimental results that we have obtained in the study of the strong coupling between microwave photons and molecular spin ensembles [1]. Coplanar microwave resonators made of 330 nm-thick superconducting YBCO have been fabricated and tested in a wide temperature (T, 2-100 K) and magnetic field (B, 0-7 T) range [2]. We show that the measured quality factors (Q_L) significantly exceeds 10^4 below 55 K and slightly decreases for increasing fields, remaining 90% of QL(B = 0) for B = 7 T and T = 2 K. These features allow the coherent coupling of resonant photons with spin ensembles at finite temperature and magnetic field. To demonstrate this, collective strong coupling was achieved by using the spin ensemble of a DPPH organic radical placed at the magnetic antinode of the fundamental mode: the in-plane magnetic field is used to tune the spin frequency gap splitting across the single-mode cavity resonance at 7.78 GHz, where clear anticrossings are observed with collective coupling rate as high as 39 MHz at T = 2 K, which is shown to scale as the square root of the number of active spins in the ensemble. 

 References [1] A. Ghirri, F. Troiani, and M. Affronte, Structure and Bonding (Springer, Berlin, 2014). [2] A. Ghirri, C. Bonizzoni, D. Gerace, S. Sanna, A. Cassinese and M. Affronte, Appl. Phys. Lett. 106, 184101 (2015).

12:30 Lunch break    
Session 3 : Arzhang Ardavan
Authors : Mario Ruben
Affiliations : INT, KIT, Karlsruhe and IPCMS, Universety of Strasbourg

Resume : Magnetic molecules have recently attracted interest in view of their potential to realize nanometre-sized (single-)molecular spintronic devices by a combination of bottom-up self-assembly and top-down lithography techniques. We report herein on the controlled generation of magnetic molecular nanostructures on conducting surfaces, partially self-assembled on sp2-carbon nano-structures (SW-CNTs, graphene, etc.), or between nano-gap gold electrodes. The obtained supramolecular devices are investigated in view of their I-V-characteristics by means of UHV- and solution-based scanning probe, break junction and electromigration techniques. [1-8] [1] S. Kyatskaya et. al. J. Am. Chem. Soc. 131, 15143-15151 (2009) [2] M. Urdampilleta et al. Nature Mater. 10, 502-506 (2011) [3] J. Schw?bel et. al. Nature Comms. 3, 953-956 (2012) [4] R. Vincent et al. Nature 488, 357-360 (2012) [5] M. Ganzhorn et al. Nature Nano. 8, 165?169 (2013) [6] M. Ruben et. al. Nature Nano. 8, 377?389 (2013) [7] S. Wagner et. al. Nature Nano. 8, 575?579 (2013) [8] S. Thiele, et al. Science, 344, 1135-1138 (2014)

Authors : Lorenzo Tesi, Eva Lucaccini, Mauro Perfetti, Elena Morra, Mario Chiesa, Matteo Mannini, Lorenzo Sorace, Roberta Sessoli
Affiliations : L. Tesi; E. Lucaccini; M. Perfetti; M. Mannini; L. Sorace; R. Sessoli Dipartimento di Chimica and UdR INSTM Universit? di Firenze E. Morra; M. Chiesa Dipartimento di Chimica Universit? di Torino

Resume : Among the several candidates for the implementation of a QIP system, mononuclear coordination complexes of transition ions are peculiarly appealing due to the relatively simple possibility of fine tuning their properties to attain improved performance and processability. In particular, systems characterized by low spin values (S=1/2) and relatively large hyperfine coupling have been recently suggested to be viable for such application.[1] They can be addressed by pulsed EPR, allowing to include multiple QBs resulting from hyperfine interactions in a single molecular assembly. We report here a combined pulsed EPR and AC susceptibility study of a VO2 containing complex, investigated in different matrices and variable concentration (frozen solution, polystirene dispersion and solid state), which shows Tm values as long as 4 microsec. and spin lattice relaxation times of 20 microsec. at 80 K. The spin-lattice relaxation times obtained by pulsed EPR measurements were compared with the outcome of ac susceptibility measurements, which show a frequency dependence of the imaginary susceptibility up to 50 K. This behaviour, which is often associated with single ion magnet behaviour, is usually considered to be in contrast with potential for QIP applications.[2] The effect of dilution and of different relaxation mechanisms were investigated and will be discussed. References [1] J.M. Zadrozny et al. J.Am.Chem.Soc. 2014,136,15841 [2] M.S. Fataftah et al. Inorg.Chem. 2014,53,10716

Authors : Kazunobu Sato,1,4 Shigeaki Nakazawa,1,4 Kenji Sugisaki,1,4 Ayaka Tanaka,1,4 Tomohiro Yoshino,1,4 Shinsuke Nishida,2,4 Tomoaki Ise,1,4 Yasushi Morita,2,4 Kazuo Toyota,1,4 Daisuke Shiomi,1,4 Masahiro Kitagawa,3,4 Satoru Yamamoto,1,4 Taiki Shibata,1 Elham Hosseini Lapasar,1,4 Koji Maruyama1,4 , Takeji Takui1,4
Affiliations : 1Graduate School of Science, Osaka City University, Osaka 558-8585, Japan 2Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan 3Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531, Japan 4FIRST-Quantum Information Processing Project, JSPS, Tokyo, Japan

Resume : The last decades have witnessed that quantum algorithms execute exponentially faster computation than classical counterparts, resulting in attempts in physical realizations of qubits from the experimental side. Among physically realized qubits documented so far, molecular electron spin-qubits have been the latest arrival, despite the fact that electron spins have naturally been anticipated as typical matter spin-qubits. This has come from some technical difficulties in molecular optimization or design which is required for qubits. Besides synthetic issues relevant to the molecular optimization, pulse-based microwave spin manipulation technology for ensemble molecular spins has been immature until recently. On these technical and methodological fronts, there have been breakthroughs by several research groups including ours [1-5]. Very recently, we have implemented NMR-paradigm electron magnetic resonance spectroscopy, in which there is no limitation on a number of pulsed microwave/RF frequency, simultaneous control of their amplitudes and relative phases of their excitation on resonance. All these technical elements are required for implementing quantum gate operations, in spite of the fact that relevant time resolution of the microwave irradiation is still limited in current technical levels. In this paper, we describe milestones reached by us in the implementation of a small scale qubit QCs/simulators (QSs) which have been based on synthetic stable molecular spins. From a viewpoint of global control of molecular spin qubits, indirect manipulation of client nuclear spin qubits by a single electron bus-spin qubit has been tested [5]. Along the line of development of the molecular spin qubits, we expect emerging important issues in the fields of QC/QIP, such as the implementation of a still small but non-trivila number of a few hundreds of spin qubits in ensemble or Lloyd model of molecular electron spins (S =1/2) embedded in periodic lattices in a one-dimensional and addressable manner. On the technical front of pulse microwave spin technology, many-body interactions require very fast time resolutions of the microwave pulse generation, and this is relevant to quantum phase estimation procedure, which we believe is important in implementing quantum chemistry/quantum chemical calculations on QCs, termed QC/QCC-on-QCs. This requirement is also relevant to developing adiabatic quantum computers (AQCs) by using molecular spins [6]. We also emphasize that a road map to QC on QCs or a significant milestone in realistic applications of QC/QIP to quantum chemistry requires disruptive improvements of quantum algorithms. [1] R. Rahimi, K. Sato, T. Takui et al., Int. J. Quantum Inf. 3, 197-204(2005). [2] K. Sato, R. Rahimi, T. Takui et al., Physica E 40, 363-366(2007). [3] K. Sato, S. Nakazawa, Y. Morita, T. Takui et al., J. Mater. Chem. 19, 3739-3754(2009). [4] S. Nakazawa, K. Sato, Y. Morita, T. Takui et al., Angew. Chem. Int. Ed. 51, 9860-9864 (2012). [5] S. Nakazawa, K. Sato, E. Hosseini, T. Takui et al., “Quantum Computing, Quantum Communication and Quantum Metrology”, (eds., Y. Yamamoto and K. Semba), Lecture Notes in Physics, Springer, 2014, in press. [6] S. Yamamoto, S. Nakazawa, K. Sugisaki, K. Sato, T. Takui, et al., Phys. Chem. Chem. Phys., 17, 2742-2749(2015). DOI: 10.1039/C4CP04744C

15:40 Coffee Break    
Poster Session : none
Authors : Judith Donner(1,2), Jan-Philipp Broschinski(3), Bastian Feldscher(3), Thorsten Glaser(3), Daniel Wegner(1,2), and Alexander Ako Khajetoorians(1)
Affiliations : 1 Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, Netherlands; 2 Physikalisches Institut and Center for Nanotechnology, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany; 3 Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie, Universität Bielefeld, Universitätsstraße 25, 33615 Bielefeld

Resume : Single-Molecule Magnets (SMMs) are potential candidates for the application in future technological devices for high-density memory storage and quantum computation. In an attempt to combine a high spin ground state and a large magnetic anisotropy in one molecule, triplesalen complexes are promising building blocks for a new generation of SMMs. The spin coupling in these molecules is based on the spin polarization effect, which requires a delocalized aromatic π system in the central carbon ring of the complex. Although the triplesalen ligand was rationally designed to convey a strong ferromagnetic coupling, magnetic measurements reveal that the coupling constants are significantly smaller than expected. Indeed, chemical analysis indicates that the central benzene ring is in a resonance hybrid of an aromatic and a non-aromatic heteroradialene form which can weaken the intramolecular spin coupling. Employing a combination of scanning tunneling microscopy (STM) and spectroscopy (STS), we have investigated single Cu3-triplesalen and Cu3-triplesalalen molecules, the latter being designed to show an enhaced intramolecular spin coupling. A thorough spectroscopic analysis reveals that small changes in the ligand structure can have a drastic influence: while the metal centers in Cu3-triplesalalen are efficiently coupled via the central carbon ring, the ones in Cu3-triplesalen are not. Thus, the spin coupling in these molecules is very sensitively dependent on the organic ligand, a finding that opens the way for an improved rational design of future SMMs.

Authors : Yasuhiko Yukawa, Satoshi Igarashi, Ayako Hosoi, Haruka Ikeda, Floriana Tuna, Guillem Aromí
Affiliations : Niigata University Japan; The University of Manchester, UK; University of Barcelona, Spain

Resume : Complexes of 3d-4f have attracted special attention because of their versatile magnetic behavior, including single molecule magnets. Such clusters may be perceived as potential spin carriers for realizing spin-based quantum bits if they exhibit an appropriate two level magnetic ground state. Several cluster nanomagnets have been prepared as good candidates for realizing spin-based qubits. An amino acid can be regarded as a typical multidentate ligand, suitable for the synthesis of heteronuclear complexes. By controlling synthetic conditions, ratio of metals, and the combination of metals and amino acids, various complexes with different structures and properties can be easily obtained. Here we describe several categories of complexes: Cu6-Na, Cu4-Na-Gd, Ni6-Gd, Ni2-Gd2 and Ni6-Gd2. Cu6-Na showed one Na+ ion trapped in the center linked to the Cu atoms of four bis(prolinato)copper units with 8 oxygen donors from the L-prolinato ligands. These four Cu atoms form an octahedron along with two further Cu ion centers. Cu4-Na-Gd was connected by a Gd ion displacing two Cu ions of top and bottom of the octahedron. Ni6-Gd, contains a central icosahedrally coordinated Gd surrounded by an octahedron of Ni centres, the second is an alternately cyclic tetranuclear Ni2Gd2 complex and the third is dinuclear Gd complex encapsulated by two of Ni3 moieties. The potential of the above versatile class of clusters for realizing spin-based qubits will be discussed.

Authors : Guillem Aromí,1 Jorge Salinas-Uber,1 Leoní A. Barrios,1 Ivana Borilovic,1 EricJ. L. McInnes,2 Amgalanbaatar Baldansuren,2 Olivier Roubeau3
Affiliations : 1. Departament de Química Inorgànica, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain. 2. The Photon Science Institute, EPSRC National EPR Facility and Service, School of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL 3. Instituto de Ciencia de Materiales de Arago´n (ICMA), CSIC and Universidad de Zaragoza, Plaza San Francisco s/n, 50009, Zaragoza, Spain

Resume : The use of molecular spins to embody qubits and qugates represents a very promising proposition for the realization the quantum processing of information [1,2]. The implementation of this technology requires the input of synthetic chemists as the source of the appropriate physical entities bound to bring about this task [3]. We have prepared a series of cluster coordination molecules containing pairs of strongly magnetically exchanged [NiCu] units with well isolated magnetic doublets in the ground state, thus constituting good realizations of qubits [4]. The quantum entanglement between both qubits in these molecules can be probed by chemically tuning the extent of the magnetic coupling between them. In addition, a molecule exhibiting two non equivalent [NiCu] S=1/2 qubits has been prepared as a possible prototype of a CNOT quantum gate, which requires two distinct qubits coupled through a weak interaction. [1] J. Mater. Chem., 2009, 19, 1754–1760 [2] Chem. Soc. Rev., 2011, 40, 3067–3075 [3] Chem. Soc. Rev. 2012, 41, 537–546 [4] Chem., Eur. J. 2009, 15, 11235-11243.

Authors : Shefali Vaidya, Maheswaran Shanmugam
Affiliations : Shefali Vaidya; Maheswaran Shanmugam

Resume : Single Ion magnetism (SIM) started in lanthanides with the observation of slow magnetic relaxation for a terbium bisphthalocyaninato complex in 2003 [1]. After that a number of lanthanide based SIM were reported in literature. But the underlying problem with lanthanide based SIM and SMM is QTM which reduces the large energy barrier observed for them [2]. In transition metal based SMMs both D and S play a crucial role. But it has been found that when D is increased, S decreases and vice a versa [3]. Another problem associated with transition metal based SMMs is the quenching of spin orbital coupling (SOC) by the ligand field. This problem can be overcome by designing SIM consisting of transition metals in which the co-ordination number is low, usually 2 or 4 (decreases the quenching of SOC). In literature it can be found that the 2 co-ordinate Ni(I), Fe(I) and Fe(II) have huge D values [4]. Among transition metal ions Co(II) based complexes play an crucial role towards the synthesis of SIM, as they possess non-integer spin ground state, which reduces the QTM [5]. In this line of interest four novel Co(II) tetrahedral complexes are synthesised and are studied both experimentally and computationally to rationalise for the synthesis of new generation of Co(II) tetrahedral complexes based SIMs. References:- 1) N. Ishikawa, M. Sugita, T. Ishikawa, S.-Y. Koshihara and Y. Kaizu, J. Am. Chem. Soc. 2003, 125, 8694-8695 2) a) M. A. AlDamen, J. M. Clemente-Juan, E. Coronado, C. Marti-Gastaldo and A. Gaita-Arino, J. Am. Chem. Soc. 2008, 130, 8874-8875. b) S. Cardona-Serra, J. M. Clemente-Juan, E. Coronado, A. Gaita-Arino, A. Camon, M. Evangelisti, F. Luis, M. J. Martinez-Perez and J. Sese, J. Am. Chem. Soc. 2012, 134, 14982-14990. 3) a) A. M. Ako, I. J. Hewitt, V. Mereacre, R. Clerac, W. Wernsdorfer, C. E. Anson and A. K. Powell, Angew. Chem., Int. Ed. 2006, 45, 4926-4929. b) C. J. Milios, R. Inglis, A. Vinslava, R. Bagai, W. Wernsdorfer, S. Parsons, S. P. Perlepes, G. Christou and E. K. Brechin, J. Am. Chem. Soc. 2007, 129, 12505-12511. 4) a) J. M. Zadrozny, M. Atanasov, A. M. Bryan, C.-Y. Lin, B. D. Rekken, P. P. Power, F. Neese and J. R. Long, Chem. Sci. 2013, 4, 125-138; b) J. M. Zadrozny, D. J. Xiao, M. Atanasov, G. J. Long, F. Grandjean, F. Neese and J. R. Long, Nat. Chem. 2013, 5, 577-581 5) G. J. Long, Inorg. Chem. 2013, 52, 13123-13131 6) H. A. Kramers, Proc. R. Acad. Sci. Amsterdam. 1930, 33, 959-972. Acknowledgements: Department of Science and Technology, Council for Scientific and Industrial Research and IIT Bombay for financial support.

Authors : A. Ghirri^1, C. Bonizzoni^2, D. Gerace^3, S. Sanna^3, A. Cassinese^4, M. Affronte^2
Affiliations : 1^Istituto Nanoscienze - CNR, Centro S3, via Campi 213/a, 41125 Modena, Italy 2^Dipartimento Fisica, Informatica e Matematica, Universita di Modena e Reggio Emilia and Istituto Nanoscienze - CNR, Centro S3, via Campi 213/a, 41125 Modena, Italy 3^Dipartimento di Fisica, Universita di Pavia, via Bassi 6, 27100 Pavia, Italy 4^CNR-SPIN and Dipartimento di Fisica, Universita di Napoli Federico II, 80138 Napoli, Italy

Resume : Strong coupling experiments with microwave photons and spin ensembles require the application of an external magnetic field to manipulate the Zeeman energy levels of the spin system. Superconducting coplanar circuits can be used to generate resonances with high quality factor (Q_L). However, for conventional superconductors such as Nb, the dissipation mechanism associated with penetration and motion of vortices degrades Q_L already at relatively low applied magnetic fields [1]. Here we report fabrication and characterization of high critical temperature YBCO superconducting coplanar resonators [2]. These devices were fabricated by optical lithography upon wet etching of YBa2Cu3O7/sapphire films. Below the superconducting transition of the YBCO film (Tc=87 K), the transmission spectrum shows a well-defined resonance centered at 7.75 GHz. The quality factor increases from Q_L≃10000 at 55 K to Q_L>20000 at 2 K. Close to Tc, measurements of the transition spectrum under applied magnetic field up to 7 T show a progressive decrease of Q_L. Conversely, at 2 K the transmission resonance is remarkably stable and Q_L (7 T) = 90% Q_L (0 T). References: [1] A. Ghirri, C. Bonizzoni, M. Righi, F. Fedele, G. Timco, R. E. P. Winpenny and M. Affronte, Appl. Magn. Reson. (2015); doi: 10.1007/s00723-015-0672-5. [2] A. Ghirri, C. Bonizzoni, D. Gerace, S. Sanna, A. Cassinese and M. Affronte, Appl. Phys. Lett. 106, 184101 (2015)

Authors : Diego Gella, Angel Domingo, Natalia Lera, Pablo J. Alonso, Fernando Luis, Olivier Roubeau
Affiliations : Instituto de Ciencia de Materiales de Aragón (ICMA), CSIC and Universidad de Zaragoza, Plaza San Francisco s/n, 50009 Zaragoza, Spain

Resume : An alternative and promising proposal for realizing quantum information processing relies on using paramagnetic species within molecular entities to embody addressable spin qubits.[1,2] Coordination chemistry provides means to dispose different metal ions within a molecule, of particular interest to realize multiple qubit structures required for specific qugates.[2] We focus here on linear trinuclear [CuLnCu] complexes [3] that, depending on their composition, can provide the adequate topology for the realization of various 2- and 3-qubit qugates. The low temperature static and dynamic magnetic properties and heat capacity of the La and Er analogues were measured and analysed to determine the corresponding energy level schemes. On basis of these, we discuss the potential of these molecules to implement CNOT and CCNOT (or Toffoli) quantum gate operations. The presence of inequivalent g factors of the Cu(II) ions and of a weak antiferromagnetic exchange coupling in [CuLaCu] allows us to propose its use as a CNOT qugate. In [CuErCu], the additional spin states associated with the Er(III) electronic ground state doublet and its weak antiferromagnetic interaction with both Cu(II) ions give rise to an energy level scheme suitable for the realization of a CCNOT gate, which forms the basis for some quantum error correction protocols, as well as of a universal three-qubit processor. [1] Chem. Soc. Rev. 2011, 40, 3067 [2] Chem. Soc. Rev. 2012, 41, 537 [3] Inorg. Chem. 2004, 43, 4435

Authors : L. Escalera-Moreno(1), D. Freedman(2), A. Gaita-Ariño(1), N. Suaud(3)
Affiliations : (1)-Instituto de Ciencia Molecular, Universidad de Valencia, c/ José Beltrán nº2 46980 Paterna, España; (2)-Department of Chemistry, Northwestern University, Evanston, IL 60208, US; (3)-IRSAMC, Universitè Paul Sabatier, 118, route de Narbonne – 31062 Toulouse Cedex 09 - France

Resume : One of the candidates to implement the concept of qubit is the qubit based on molecular electron spin [1-3]. Molecularly, one of the mechanisms of quantum decoherence is [4] phonon - electron spin coupling. In order to shed light to design high quantum coherence molecules and deepen the theoretical understanding of this mechanism, we base our research on two Mn+2 complexes (synthesized and under experimental study). Specifically, we study the coupling between the electron ground sextet and the vibrational modes of each complex. We then compare how the coupling changes as the rigidity is increased from the less rigid complex to the more rigid one. It is important to realize that these complexes have been conceived such that the main difference between them is the vibrational spectrum. Thus, we may assure that the main weight regarding quantum decoherence comes precisely from the mechanism that we want to study. Namely, from two complexes that are chemically and magnetically very similar, the most important difference is the rigidity. So, our hypothesis is that such rigidity might be the dominating factor regarding the difference of quantum decoherence between the complexes [5]. [1] J. Lehmann et al., J. Mater. Chem. 19 (2009) 1672-1677 [2] D. Stepanenko et al., Inorganica Chimica Acta 361 (2008) 3740-3745 [3] Michael N. Leuenberger, D. Loss, Nature 410 (2001) 789-793 [4] S. Takahashi et al., Nature 476 (2011) 76-79 [5] K. Bader et al., Nature Communications 5 (2014) 5304

Authors : Leoni A. Barrios 1, Verónica Velasco1, David Aguilà 1-2, Guillem Aromí 1, Olivier Roubeau 3, Fernando Luis 3.
Affiliations : 1 Departament de Química Inorgànica, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain; 2 CNRS, CRPP and University of Bordeaux, UPR 8641, Pessac, F­33600, France; 3 Instituto de Ciencia de Materiales de Aragón (ICMA) and Departamento de Física de la Materia Condensada, CSIC, ­Universidad de Zaragoza E­50009 Zaragoza, Spain

Resume : For some years, we have focused on the design, synthesis and study of molecular coordination complexes of lanthanides as qubits and qugates for quantum computation (1,2). In the case of dinuclear complexes, the dissimilarity between the metallic centers, the weak interaction between them and the long decoherence times are necessary requirements in order to implement these molecular systems as prototypes capable to realize 2qubit quantum operations (3, 4). Inspired by recent promising results (1), where the dimer [CeEr(HL)2(H2L)(NO3)(py)(H2O)] was shown to exhibit the requirements to act as 2-qubit spin quantum processor and quantum coherence of qugate operations, the present work elaborates on the preparation and use of several extended beta-diketone organic ligands, 1,3-bis(3-oxo-3-(naphtyl)-propionyl)-2-pyridine (H2LA), 6-[3-(naphthalen-2-yl)-3-oxopropanoyl]pyridine-2-carboxylic acid (H2LB) and 6-[3-(1-hydroxynaphthalen-2-yl)-3-oxopropanoyl]pyridine-2-carboxylic acid (H3LC), designed to prepare new multinuclear heterometallic molecular architectures. Some such species are [CeHo2(LA)2(LB)2(H2O)2(py)]NO3, [CeEr2(LA)2(LB)2(H2O)2(py)]NO3, [La2Dy3(LA)3(LB)4]NO3, or [CeHo(H2LC)(HLC)2(H2O)(py)]NO3. These species are trinuclear [LnLn’Ln], pentanuclear [LnLn’LnLn’Ln] or novel dinuclear [LnLn’]. The former could be explored to implement error correction algorithms (5), the latter allow to tune processability and the metal environments in order optimize the quantum gate performance. 1.- J. Am. Chem. Soc. 2014, 136, 14215−14222. 2.- PRL 107, 117203 (2011) 3.- Inorg. Chem. 2010, 49, 6784–6786. 4.- Chem. Soc. Rev., 2012, 41,537–546. 5.- EPL, 110 (2015) 33001.

Authors : C. Extremiana,1 M. D. Jenkins,1 U. Naether,1 M. Ciria,1 J. Sesé,2 M. C. Pallarés,2 A. Lostao,2,3 J. Atkinson,4 C. Sánchez-Azqueta,5 E. del Barco,4 J. Majer,6 D. Zueco,1,3 J. L. García-Palacios,1,3 and F. Luis1
Affiliations : 1Instituto de Ciencia de Materiales de Aragón, CSIC-Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain 2Laboratorio de Microscopías Avanzadas. Instituto de Nanociencia de Aragón, Universidad de Zaragoza, 50018 Zaragoza, Spain 3Fundación ARAID, Campus Río Ebro, 50018 Zaragoza, Spain 4Department of Physics, University of Central Florida, Orlando, Florida 32816, USA 5Dpto. de Ingeniería Electrónica y Telecomunicaciones, Universidad de Zaragoza, 50009 Zaragoza, Spain 6Vienna Center for Quantum Science and Technology, Atominstitut, TU Wien, 1020 Vienna, Austria

Resume : The field of cavity quantum electrodynamics (QED) studies the interaction of photons in resonant cavities with either natural or “artificial” atoms, such as quantum dots and superconducting qubits, having a nonlinear and discrete energy level spectrum. For applications in spectroscopy and especially quantum information processing, a major goal is to maximize the coupling strength g of the atom to either electric or magnetic cavity fields, making it larger than the decoherence rates of both the cavity and the atom (strong coupling regime). Attaining this regime for individual spin qubits would open the possibility of developing an all-magnetic quantum processor. Although still very challenging, this goal appears to be within reach of state-of-the art technology provided that resonant circuits able to concentrate the RF magnetic field in nanoscopic regions can be fabricated. In this communication, we report on the design, fabrication, and characterization of superconducting coplanar waveguide resonators with nanoscopic constrictions. By reducing the size of the center line down to 50 nm, the radio frequency currents are concentrated and the magnetic field in its vicinity is increased. The device characteristics are only slightly modified by the constrictions, with changes in resonance frequency lower than 1% and internal quality factors of the same order of magnitude as the original ones. These devices could enable the achievement of higher couplings to small magnetic samples or even to single molecular spins and have applications in circuit quantum electrodynamics, quantum computing, and electron paramagnetic resonance. Preliminary experiments performed on small spin ensembles directly deposited onto these constrictions by dip pen nanolithography are also reported.

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Session 5 : Andrea Morello
Authors : Stephen Hill, Muhandis Shiddiq, Dorsa Komijani, Yan Duan, Salvador Cardona-Serra, Alejandro Gaita-Ariño, Eugenio Coronado
Affiliations : Department of Physics and NHMFL, Florida State University, Tallahassee, FL 32310, USA; Instituto de Ciencia Molecular, Universidad de Valencia, Poligono la Coma s/n, 46980 Paterna, Spain

Resume : We outline a strategy for protecting molecular spin qubits against one of the more stubborn sources of decoherence in solids—that of dipolar fluctuations associated with the electron and nuclear spin baths. Continuous-wave (cw) and pulsed EPR studies of a Ho(III) ion encapsulated within a polyoxometallate (POM) cage will be presented. The J = L + S = 8 spin-orbit coupled ground state of the Ho ion experiences significant magnetic anisotropy due to the POM ligand field. Its approximate D4d symmetry results in a low-lying pair of mJ = ±4 singlets. High-frequency cw EPR studies reveal an eight line spectrum corresponding to transitions between the mJ = ±4 states, split by a strong hyperfine interaction with the I = 7/2 Ho nucleus. Low-frequency studies reveal a series of avoided crossings between the 16 lowest-lying electron-nuclear sub-levels, leading to a highly non-linear field-dependence of the spectrum. Electron-spin-echo measurements allow detailed studies of the coherent electron-nuclear spin dynamics and evaluation of the phase memory time T2. Remarkably long T2 values are found, even for the most concentrated samples. Results are analyzed for different hyperfine transitions and Ho concentrations. The long T2 times are attributed to the non-linear field effects that give rise to optimal operating points in the EPR spectrum that are insensitive to the applied field and, hence, immune to dipolar field fluctuations. These are the so-called atomic clock transitions.

Authors : David Aguilà,1,2 Leoní Barrios,1 Verónica Velasco,1 Olivier Roubeau,3 Ana Repollés,3 Pablo J. Alonso,3 Javier Sesé,4 Simon J. Teat,5 Fernando Luis,3 Guillem Aromí1
Affiliations : 1 Departament de Química Inorgànica, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain; 2 CNRS, CRPP and University of Bordeaux, UPR 8641, Pessac, F-33600, France; 3 Instituto de Ciencia de Materiales de Aragón (ICMA) and Departamento de Física de la Materia Condensada, CSIC-Universidad de Zaragoza E-50009 Zaragoza, Spain ; 4 Instituto de Nanociencia de Aragón and Departamento de Física de la Materia Condensada, Universidad de Zaragoza, E-50018 Zaragoza, Spain ; 5 Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States

Resume : The search of solid-state candidates for the physical implementation of quantum computing is one of the biggest challenges in nanoscience. In this respect, the proposal of using magnetic molecular systems is very attractive in terms of scalability and flexibility since identical magnetic molecules can be prepared and tuned via simple chemical methods.[1,2] Concretely, complexes featuring 4f metal ions are particularly interesting since lanthanide centres exhibiting a doubly degenerate magnetic ground state appears as a convenient realization of the spin quantum bit. By using the asymmetric ligand 6-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-2-pyrdinecarboxylic acid (H3L), we have developed a method to obtain pure dinuclear homo- and heterometallic 4f-4f’ complexes from one-pot reaction.[3,4] From all of the possible combinations, complex containing Ce(III) and Er(III) entails ideal properties for its application as a molecular quantum processor, since the two lanthanide ions have a different magnetic ground state and present mainly zero nuclear spin. Magnetic susceptibility, specific heat and EPR measurements have been carried out to demonstrate that both metals behave as quantum bits, while the energy eigenstates derived from the weak coupling between them can be used to perform universal two-qubit logic operations.[4] 1. Nature 410, 789 (2001) 2. Chem. Soc. Rev. 41, 537 (2012) 3. Chem. Eur. J., 19, 5881 (2013) 4. J. Am. Chem. Soc., 136, 14215 (2014)

Authors : A. Repollés,a M. C. Pallarés,b D. Gella,a V. Velasco,c M. Jenkins,a D. Aguilà,c O. Roubeau,a A. Lostao,b,d L. Barrios,c J. Sesé,b D. Drung,e Th. Schurig,e G. Aromí,c and F. Luisa
Affiliations : a Instituto de Ciencia de Materiales de Aragón, CSIC-Univ. Zaragoza, 50009 Zaragoza, Spain b Laboratorio de Microscopías Avanzadas, Instituto de Nanociencia de Aragón, Universidad de Zaragoza, 50018 Zaragoza, Spain c Departament de Química Inorgànica, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain d Fundación ARAID, Campus Río Ebro, 50018 Zaragoza, Spain e Physikalisch-Technische Bundesanstalt, 10587 Berlin, Germany

Resume : The application of single molecule magnets to quantum information necessarily involves their rational integration into solid state devices, such as SQUIDs or superconducting resonators. An intriguing question is then how the loss of crystal order and the interaction with the substrate affect the relevant magnetic properties. Here, we report the results of ac susceptibility measurements performed, down to very low temperatures (T > 13 mK), on thin layers of Dy2 asymmetric molecular clusters, which are candidates to realize 2-qubit gates. The molecules are integrated into a micro-SQUID susceptometer by means of Dip Pen Nanolithography, without the need of any previous functionalization of neither the molecule nor the substrate. Frequency-dependent susceptibility data measured on 4 and 20 molecular layers thick films are compared with similar results obtained for bulk polycrystalline samples. These experiments provide direct information on the single-ion magnetic anisotropies and the intra-molecular coupling between the two lanthanide spins, which are crucial ingredients for the realization of a CNOT gate. The results show that the molecular Dy2 units largely remain intact at the surface. Low-nuclearity lanthanide magnetic clusters are therefore robust against distortions caused by the molecule-substrate interactions and thus might provide suitable building blocks for the development of a scalable quantum architecture.

10:30 Coffee Break    
Session 6 : Filippo Troiani
Authors : Paolo Santini
Affiliations : Dipartimento di Fisica e Scienze della Terra, Università di Parma (Italy)

Resume : Two-qubit gates represent the greatest challenge in using molecular nanomagnets for quantum-information processing because, ideally, these gates call for switchable qubit-qubit interactions. This problem can be bypassed by exploiting auxiliary, non-computational units, whose states are controlled by the user to induce the requested dynamics on the qubits, thus mimicking the effect of a switchable interaction [1]. Dimers of Cr7Ni rings linked through Ni and Co complexes have been recently synthesized with magnetic couplings engineered in order to fit the requirements of this scheme [2,3]. Qubits are encoded in the Cr7Ni ground doublet, and the ion interposed between the qubits is used to effectively switch the qubit-qubit interaction, thus allowing for scalable single- and two-qubit gates. Several Cr7Ni-Ni-Cr7Ni variants with different geometry are studied by means of a recently developed [4] DFT approach and their spin Hamiltonians are deduced systematically. In addition, a Cr7Ni-Co-Cr7Ni variant has been characterized by means of Q- and W-band EPR spectroscopy. Both Ni and Co variants can be used for proof-of-principle quantum simulations. The anisotropic qubit-switch exchange of the Co variant, together with the perpendicular arrangement of the two rings, makes the two qubits significantly inequivalent. This enables each of the two qubits to be separately addressed and makes the complex well suited for the implementation of CNOT gates and for the quantum simulation of antisymmetric Hamiltonians. [1] P. Santini et al., Phys. Rev. Lett., 2011, 107, 230502. [2] A. Chiesa et al., Sci. Rep. [3] J. Ferrando-Soria et al., in preparation [4] A. Chiesa et al., Phys. Rev. Lett., 2013, 110, 157204.

Authors : Michael J. Graham, Joseph M. Zadrozny, Majed S. Fataftah, Danna E. Freedman
Affiliations : Northwestern University

Resume : Employing electronic spin for quantum computation necessitates developing rational design principles for the synthesis of magnetic molecules and materials that are suitable as qubits. Towards that end, we are developing series of molecules where a single variable can be manipulated to determine its impact on qubit viability. Studies of spin, phonon effects, and hyperfine coupling will be presented.

Authors : J. J. Baldoví,1 E. Coronado,1 L. Escalera,1 D. Freedman,2 A. Gaita-Ariño,1* S. Hill,3 L. E. Rosaleny-Peralvo,1 N. Suaud 4
Affiliations : 1 ICMol, Universidad de Valencia, c/ J. Beltrán Martínez nº 2 46980 Paterna, España 2 Dept. of Chemistry, Northwestern University, Evanston, IL 60208, USA 3 NHMFL, 1800 E. Paul Dirac Dr, Tallahassee, FL 32310, USA 4 IRSAMC, Universitè Paul Sabatier, 118, route de Narbonne - 31062 Toulouse Cedex 09 - France

Resume : We will present recent advances in this sub-field, namely: 1.- Ab initio calculation of the coupling between molecular vibrations and the spin energy levels, and subsequent estimation of vibrational decoherence in different molecular spin qubits. 2.- Development and improvement of a low-cost, effective electrostatic computational tool (SIMPRE) to estimate energy levels and wave functions for molecular spin qubit candidates, now including the relation between the effective parameters and chemical concepts such as electronegativity and coordination number 3.- Extension of SIMPRE to estimate the decoherence caused by the coupling to the nuclear spin bath, and application of this new tool to a challenging proposal: the use of biopolymers as programmable scaffold for the complex organization of molecular spin qubits.

12:40 Lunch Break    
Session 7 : Olivier Roubeau
Authors : F. Troiani (1), I. Siloi (2), P. Zanardi (3)
Affiliations : (1) CNR, S3-Istituto Nanoscienze, Modena (Italy) (2) Università di Modena e Reggio Emilia, Modena (Italy) (3) University of Southern California, Los Angeles, California, USA

Resume : Nanomagnets represent a varied class of molecular spin clusters, whose physical properties can be widely tuned at the chemical level. Spin clusters with dominant exchange interaction are characterized by highly entangled ground states. Besides, quantum coherence has been observed in the spin dynamics of different nanomagnets, suggesting the possibility of applications in quantum technologies. In this perspective, a deep understanding and a quantitative characterization of the non-classical features is essential. In this talk, I will provide a theoretical description of quantum entanglement in molecular spin clusters, with specific reference to antiferromagnetic rings. The detection of entanglement in terms of experimentally accessible quantities will also be discussed, as well as the engineering of entanglement by means of chemical substitutions. Also Schroedinger-cat states represent prototypical examples of nonclassical states. The size of such states, generated in a variety of nanomagnets, will be quantified by means of quantum-information theoretical measures, and possible applications in quantum technologies will be discussed.

Authors : Elena Garlatti, Giuseppe Amoretti, Stefano Carretta, Paolo Santini, Morten A. Albring, , Rebecca J. Docherty, George F. S. Whitehead, Robin G. Pritchard, Grigore A. Timco, Floriana Tuna, Eric J. McInnes, David Collison, Richard E. P. Winpenny, Tatiana Guidi, Victoria Garcia Sakai, Giulia Lorusso, Marco Affronte, Michael L. Baker , Hannu Mutka
Affiliations : Dipartimento di Fisica e Scienze della Terra, Università di Parma, Parco Area delle Scienze 7/a, 43124 Parma, Italy; Dipartimento di Fisica e Scienze della Terra, Università di Parma, Parco Area delle Scienze 7/a, 43124 Parma, Italy; Dipartimento di Fisica e Scienze della Terra, Università di Parma, Parco Area delle Scienze 7/a, 43124 Parma, Italy; Dipartimento di Fisica e Scienze della Terra, Università di Parma, Parco Area delle Scienze 7/a, 43124 Parma, Italy;School of Chemistry and Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom; School of Chemistry and Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom; School of Chemistry and Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom; School of Chemistry and Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom; School of Chemistry and Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom; School of Chemistry and Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom; School of Chemistry and Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom; School of Chemistry and Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom; School of Chemistry and Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom; ISIS Facility, Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom; ISIS Facility, Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom; Istituto de Ciencia de Materiales de Aragón, CSIC-Universidad de Zaragoza, Departamento de Fıś ica de la Materia Condensada, 50009 Zaragoza, Spain; Dipartimento di Fisica, Università di Modena e Reggio Emilia, via Campi 213/a, 41100 Modena, Italy; Institut Laue-Langevin, BP 156, 6 rue Jules Horowitz, 38042 Grenoble Cedex 9, France; Institut Laue-Langevin, BP 156, 6 rue Jules Horowitz, 38042 Grenoble Cedex 9, France.

Resume : Molecular nanomagnets are considered promising qubits for spin-based quantum information processing (QIP) [1] and they can also be linked together [2] in order to realize supramolecular structures fitting specific QIP schemes. Understanding the spin dynamics of these systems and exploit them for QIP applications is at present a major goal in the field of molecular magnetism. In this work we study the family of {Cr7M} “purple” rings [M = Zn, Mn, Ni] and a new family of “purple-green” dimers [3]. By using complementary experimental techniques, including magnetization and specific heat measurements, inelastic neutron scattering and EPR spectroscopy, we investigate the magnetic features and spin dynamics of these systems. The first issue we address is to find a minimum set of parameters of the microscopic spin Hamiltonian describing a broad set of data on single rings, then we examine whether these parameters are transferable between similar structures, comparing them with those of “green” {Cr7M} rings. From the comparison of our calculations with experimental data we also investigate the interaction between two rings in purple-green dimers, in order to envisage their application in QIP. [1] P. Santini et al., Phys. Rev. Lett. 107, 230502 (2011). [2] G. A. Timco et al., Nat. Nanotechnol. 4, 173 (2009). [3] E. Garlatti, et al., J. Am. Chem. Soc. 136, 9763 (2014). Acknowledgements: This work was financially supported by the Italian FIRB Project RBFR12RPD1 of the Italian MIUR.

Authors : José J. Baldoví, Yan Duan, Alejandro Gaita-Ariño, Eugenio Coronado
Affiliations : Instituto de Ciencia Molecular (ICMol), Universidad de Valencia, C/Catedrático José Beltrán 2, E-46980 Paterna, Spain.

Resume : Lanthanide single-ion magnets (SIMs) have excited researchers working in molecular magnetism over the past decade due to their attractive physical properties. The magnetic and quantum properties of SIMs depend primarily on the anisotropy of a single ion, which results from a strong spin-orbit coupling and an adequate ligand field. In spite of the theoretical efforts to fully understand their behaviour, modelling the magnetic and spectroscopic properties of f-element complexes still remains a challenge. Commonly, these systems have been explained by crystal field theory, which unfortunately requires the determination of a large number of crystal field parameters (CFPs). [1] A different strategy involves the direct calculation of CFPs using the real structure of the compounds. These methods include Complete Active Space ab initio calculations (CASSCF and CASPT2) [2] and effective electrostatic models, such as the semiempirical Radial Effective Charge (REC) model [3]. In this contribution, we present a series of new SIMs that are used as model systems to test the predictive capabilities of these standard tools in the field. For that, we take advantage of the spectroscopic studies [4] and angular dependence of the single-crystal magnetic susceptibility carried out on these complexes [5]. In this process, we also study the thermal structure effects in a β-diketonate SIM, whose structure has been determined at different temperatures.

Authors : Jesús Ferrando-Soria,Eufemio Moreno Pineda, Antonio Fernandez, Alessandro Chiesa, Stefano Carretta, Paolo Santini, Grigore A. Timco, Eric J. L. McInnes and Richard E. P. Winpenny
Affiliations : Alessandro Chiesa; Stefano Carretta; Paolo Santini :Dipartimento di Fisica e Scienze della Terra, Università di Parma, viale delle Scienze 7/a, 43123 Parma, Italy. Jesús Ferrando-Soria; Eufemio Moreno Pineda; Antonio Fernandez; Grigore A. Timco; Eric J. L. McInnes; Richard E. P. Winpenny:School of Chemistry and Photon Science Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom.

Resume : The physical implementation of quantum information processing relies on obtaining quantum bits and quantum gates that could be organized in such a way to carry out useful algorithms. To build useful devices two universal gates are needed – the CNOT gate and the SWAP gate. To achieve such gates it would be ideal if one simple module could be used in each, linked and addressed in different ways to achieve the gate operations. Here we show, as proof of principle, that {Cr7Ni} rings can be functionalized to provide modules that can be easily assembled into these two types of two-qubit gates; we fully characterize the two-qubit gates and use these parameters to perform simple simulations that indicate how such gates would operate. This provides a strong basis for future developments of molecular two-qubit gates towards quantum computation.

Authors : Enrique del Barco
Affiliations : Physics Department, University of Central Florida, Orlando USA

Resume : I will present a recent work done in collaboration with Christian A. Nijhuis (Graphene Research Centre / National University of Singapore) where we discuss the range of validity of coherent versus incoherent theory treatments for the understanding of some recent experimental results obtained in molecular tunnel junctions and employ them to determine some noteworthy characteristics of the junctions in view of potential applications in molecular electronics. Specifically, I will discuss single-level transport models employed to explain experiments performed in SAM-based EGaIn junctions of S(CH2)nFcC13-n electrical rectifying molecules in where the Ferrocene (Fc) unit is placed at different positions (n) within the alkyl chain, enabling the determination of the electrostatic potential profile in the junction, which we find highly non-linear.

15:45 Concluding Remarks    
15:55 Coffee break    
18:00 Best Student Presentation Awards Ceremony and Reception (Main Hall)    

No abstract for this day

Symposium organizers
Guillem AROMÍ BEDMARUniversitat de Barcelona

Diagonal 645 Barcelona Spain

+34 934039760
Olivier ROUBEAU CSIC-Universidad de Zaragoza

Pedro Cerbuna 12 50009 Zaragoza Spain

+34 976762461
Richard E. P. WINPENNYUniversity of Manchester

Oxford Road Manchester M13 9PL UK

+44 0161 275-4654
Danna E. FREEDMAN Northwestern University

Evanston, Illinois 60208 USA

+1 (847) 491-4441