2,500 research outputs found
Environment-induced sudden transition in quantum discord dynamics
Non-classical correlations play a crucial role in the development of quantum
information science. The recent discovery that non-classical correlations can
be present even in separable (unentangled) states has broadened this scenario.
This generalized quantum correlation has been increasing relevance in several
fields, among them quantum communication, quantum computation, quantum phase
transitions, and biological systems. We demonstrate here the occurrence of the
sudden-change phenomenon and immunity against some sources of noise for the
quantum discord and its classical counterpart, in a room temperature nuclear
magnetic resonance setup. The experiment is performed in a decohering
environment causing loss of phase relations among the energy eigenstates and
exchange of energy between system and environment, resulting in relaxation to a
Gibbs ensemble
Geometrical bounds on irreversibility in open quantum systems
Clausius inequality has deep implications for reversibility and the arrow of
time. Quantum theory is able to extend this result for closed systems by
inspecting the trajectory of the density matrix on its manifold. Here we show
that this approach can provide an upper and lower bound to the irreversible
entropy production for open quantum systems as well. These provide insights on
the thermodynamics of the information erasure. Limits of the applicability of
our bounds are discussed, and demonstrated in a quantum photonic simulator
Quantum Simulation of single-qubit thermometry using linear optics
Standard thermometry employs the thermalisation of a probe with the system of
interest. This approach can be extended by incorporating the possibility of
using the non-equilibrium states of the probe, and the presence of coherence.
Here, we illustrate how these concepts apply to the single-qubit thermometer
introduced by Jevtic et al. by performing a simulation of the qubit-environment
interaction in a linear-optical device. We discuss the role of the coherence,
and how this affects the usefulness of non-equilibrium conditions. The origin
of the observed behaviour is traced back to the propensity to thermalisation,
as captured by the Helmholtz free energy.Comment: 6 pages, 6 figure
Hierarchy in temporal quantum correlations
Einstein-Podolsky-Rosen (EPR) steering is an intermediate quantum correlation
that lies in between entanglement and Bell non-locality. Its temporal analogue,
temporal steering, has recently been shown to have applications in quantum
information and open quantum systems. Here, we show that there exists a
hierarchy among the three temporal quantum correlations: temporal
inseparability, temporal steering, and macrorealism. Given that the temporal
inseparability can be used to define a measure of quantum causality, similarly
the quantification of temporal steering can be viewed as a weaker measure of
direct cause and can be used to distinguish between direct cause and common
cause in a quantum network.Comment: 10 pages, 3 figure
Generation of Squeezed States of Nanomechanical Resonators by Reservoir Engineering
An experimental demonstration of a non-classical state of a nanomechanical
resonator is still an outstanding task. In this paper we show how the resonator
can be cooled and driven into a squeezed state by a bichromatic microwave
coupling to a charge qubit. The stationary oscillator state exhibits a reduced
noise in one of the quadrature components by a factor of 0.5 - 0.2. These
values are obtained for a 100 MHz resonator with a Q-value of 10 to 10
and for support temperatures of T 25 mK. We show that the coupling to
the charge qubit can also be used to detect the squeezed state via measurements
of the excited state population. Furthermore, by extending this measurement
procedure a complete quantum state tomography of the resonator state can be
performed. This provides a universal tool to detect a large variety of
different states and to prove the quantum nature of a nanomechanical
oscillator.Comment: 13 pages,9 figure
- …