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Information processing and networking in quantum coherent systems
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The extraordinary technological progress achieved in the past years has paved the way to direct access to the complexity in Nature, to control and to exploit it as a resource. In solid state physics the key is provided by the possibility to reach the nanoscale. Engineering and manipulating coherence at the nanoscale represents the major challenge towards quantum information processing and networking, comprising a series of important issues ranging from fundamental problems to applications. From a more theoretical point of view, this includes the problem of understanding, producing, manipulating and measuring entanglement in solid state devices. Specific questions are "quantification" of entanglement and its role in driving quantum phase transitions, a topic bridging quantum information science with critical phenomena in strongly correlated systems. From the practical point of view, one of the most important obstacles to further developments of nanometric-sized devices technology is the extreme sensitivity of nanodevices to noise. A relevant portion of the scientific activities in this direction is focused on the study of superconducting nanocircuits, displaying a series of quantum phenomena resulting from the interplay of electrostatic effects and the intrinsic phase-coherence of superconductors. One of the main tasks of research on solid state nanocircuits is to investigate the different noise sources, with the goal to find a trade-off between flexible design and protection from decoherence. The identification of computational protocols and "quantum control" techniques appropriate to the solid state is a rapidly developing research area, forming a new sub-field of physics arising from different disciplines ranging from Quantum Optics to NMR. Tackling the broad range of problems mentioned above requires the development of sophisticated statistical mechanics techniques and numerical approaches. |
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RECENT HIGHLIGHTS by MATIS: |
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| In quantum systems the interplay between phase coherence, strong interactions, and low dimensionality may result in surprising dynamical behaviours. In this Highlight we report on our recent activity on quench dynamics phenomena occurring in the vicinity of a quantum phase transition. We generalized the so-called Kibble-Zurek mechanism for the non-equilibrium dynamics of open quantum many-body systems driven across a critical point by quenching a system parameter at a certain velocity (see figure) [1]. We addressed the problem of the thermal quench, i.e. the response of the system to a sudden change of the temperature keeping the other system control parameters fixed [2]. Some key questions we answer are: How is thermalization achieved microscopically? What are the characteristic time and length scales emerging from the out-of equilibrium dynamics? What are the dynamical signatures of the quantum phase transition? In the Ref. [3] we aim at investigating the effects of topology in the out-of-equilibrium dynamics induced by the crossing of a quantum critical point. This might be important to implement a protected quantum memory for quantum annealing protocols. | |||
| [1]
Adiabatic Dynamics in Open Quantum Critical Many-Body Systems Patanč D., Silva A., Amico L., Fazio R., and Santoro G.E. Phys. Rev. Lett. 101, 175701 (2008) - DOI: 10.1103/PhysRevLett.101.175701; Adiabatic dynamics of a quantum critical system coupled to an environment: Scaling and kinetic equation approaches Patanč D., Silva A., Amico L., Fazio R., and Santoro E. G. Phys. Rev. B 80, 024302 (2009) - DOI: 10.1103/PhysRevB.80.024302 |  |
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[2]
Thermalization dynamics close to a quantum phase transition Patanč D., Silva A., Sols F., Amico L. Phys. Rev. Lett. 102, 245701 (2009) - DOI: 10.1103/PhysRevLett.102.245701 [3] Topology-Induced Anomalous Defect Production by Crossing a Quantum Critical Point Bermudez A , Patanč D, Amico L, and Martin-Delgado M-A Phys. Rev. Lett. 102, 135702 (2009) - DOI: 10.1103/PhysRevLett.102.135702 |
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| We consider the transfer of quantum information down a single-mode quantum transmission line. Such a quantum channel is modeled as a damped harmonic oscillator, the interaction between the information carriers -a train of N qubits- and the oscillator being of the Jaynes-Cummings kind. We calculate a lower bound for the quantum capacity for different operating conditions and compare two protocols where memory effects are cancelled by resetting the channel after each use, and where memory effects are present but compete with damping. It is shown that in this latter case information transmission rates inclease, both for the transfer of quantum and classical private information. Our results descibe dephasing in a micromaser emerging from fluctuations in the laser field. In the solid-state scenario they may describe communication by electrons or chiral quasiparticles sent down a mesoscopic channel where they interact with optical phonons or a quantum memory in a circuit-QED setup implemented on a superconducting platform. |
Enhancement of Transmission Rates in Quantum Memory Channels with Damping Benenti G., D'Arrigo A., Falci G. Phys. Rev. Lett. 103, 020502 (2009) - DOI: 10.1103/PhysRevLett.103.020502 |  |
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| The entanglement in the ground state of a class of one dimensional quantum spin models has been studied, being highly relevant for strongly correlated statistical mechanics and able to provide a possible physical realization of a future quantum computer. In particular we identifi ed special points in the phase diagram of the system separating two regions characterized by a qualitatively different entanglement encoded in the ground state of the system; we further demonstrated that the range of the two-point entanglement diverges while approaching such points. Entanglement in many-body systems Amico L., Fazio R., Osterloh A., Vedral V. Rev. Mod. Phys. 80, 517 (2008) - DOI: 10.1103/RevModPhys.80.517 |  |
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| We have studied the measurement of higher current moments with a dissipative resonant circuit coupled inductively to a mesoscopic device in the coherent regime. Information about the higher current moments is coded in the histograms of the charge on the capacitor plates of the resonant circuit. The role of dissipation has been shown to be essential for the measured noise to remain finite. For a quantum point contact (QPC) even a very weak damping washes out the singularity of the measurable noise when the resonant frequency of the LC circuit matches the bias voltage applied to the QPC. The combination of current correlators entering the measurement of the third moment has been identified. Detection of finite frequency current moments with a dissipative resonant circuit Zazunov A., Creux M., Paladino E., Crepieux A., Martin T. Phys. Rev. Lett. 99, 066601 (2007) - DOI: 10.1103/PhysRevLett.99.066601 |
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PARTICIPANTS |
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| AMICO Luigi | 095 7382822 | ||
| BERRITTA Marco | 095 7382813 | ||
| D'ARRIGO Antonio | 095 7382813 | ||
| FALCI Giuseppe | 095 7382806 | ||
| PALADINO Elisabetta | 095 7382803 | ||