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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)

No abstract for this day

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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).

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 : 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)

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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.


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