Superconducting Nanocircuits | Quantum Dissipative Systems | Quantum communication | Coherent control of quasiparticles in graphene | Further research lines |
Quantum Dissipative Systems
When dealing with complex systems one is often interested only in the dynamics of few relevant variables out of the many degrees of freedom which provide the microscopic description. Sometimes, a convenient approach is to regard the relevant variables as describing an open system which interacts with an environment made up by all the remaining degrees of freedom. If these latter can be ``eliminated'', one is left with an effective model where only the variables of the relevant system appear. The environment enters the dynamics of the open system only via its statistical properties. The system-bath interaction manifests itself in two different ways. It induces dissipative transitions between the relevant system states (the only effect left in the classical limit), and fluctuations of the energy difference between the levels. Both these effects tend to reduce the phase correlations which are at the origin of the phase-coherent behaviour of the isolated system. As a result, phase coherence is maintained over a characteristic time scale, called the decoherence time. Environment induced decoherence, well known in the microscopic world, has striking effects in the behaviour of mesoscopic systems, and represents the major problem in the implementation of Quantum Computers. We study the decoherence effects in quantum dissipative systems which model mesoscopic devices for Quantum Computation. Two main topics are
- Decoherence induced by "linear noise", which can be modeled by an infinite bath of harmonic oscillators (Caldeira and Leggett model). In particular we focus on dissipative two-state systems.
- Decoherence originating from a "discrete" environement. We analyze the decoherence in Josephson qubits in the charge regime originating from background charges in the substrate responsible for the 1/f noise.
On a complementary perspective, mesoscopic detectors are themselves quantum dissipative systems able to perform measures on a mesoscopic system. We study dissipative resonant circuits which act as on-chip detectors of noise and higher cumulants of the current flowing in mesoscopic conductors.
RECENT HIGHLIGHTS by SMT:
Characterization of coherent impurity effects in solid-state qubits
Paladino E., Sassetti M., Falci G., Weiss U.
Phys. Rev. B 77, 041303(R) (2008)
Detection of finite-frequency photoassisted shot noise with a resonant circuit
Chevallier D., Jonckheere T., Paladino E., Falci G., and Martin T.
Phys. Rev. B 81, 205411 (2010)
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)