1,721,187 research outputs found
Cooling by heating: Very hot thermal light can significantly cool quantum systems
No full textWe introduce the idea of actually cooling quantum systems by means of incoherent thermal light, hence giving rise to a counterintuitive mechanism of "cooling by heating." In this effect, the mere incoherent occupation of a quantum mechanical mode serves as a trigger to enhance the coupling between other modes. This notion of effectively rendering states more coherent by driving with incoherent thermal quantum noise is applied here to the optomechanical setting, where this effect occurs most naturally. We discuss two ways of describing this situation, one of them making use of stochastic sampling of Gaussian quantum states with respect to stationary classical stochastic processes. The potential of experimentally demonstrating this counterintuitive effect in optomechanical systems with present technology is sketched. © 2012 American Physical Society
Opto- and electro-mechanical entanglement improved by modulation
No full textOne of the main milestones in the study of opto- and electromechanical systems is to certify entanglement between a mechanical resonator and an optical or microwave mode of a cavity field. In this work, we show how a suitable time-periodic modulation can help to achieve large degrees of entanglement, building upon the framework introduced in Mari and Eisert (2009 Phys. Rev. Lett. 103 213603). It is demonstrated that with suitable driving, the maximum degree of entanglement can be significantly enhanced, in a way exhibiting a nontrivial dependence on the specifics of the modulation. Such timedependent driving might help to experimentally achieve entangled mechanical systems also in situations when quantum correlations are otherwise suppressed by thermal noise. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
Opto- and electro-mechanical entanglement improved by modulation
Full text linkOne of the main milestones in the study of opto- and electro-mechanical
systems is to certify entanglement between a mechanical resonator and an
optical or microwave mode of a cavity field. In this work, we show how a
suitable time-periodic modulation can help to achieve large degrees of
entanglement, building upon the framework introduced in Mari and Eisert (2009
Phys. Rev. Lett. 103 213603). It is demonstrated that with suitable driving,
the maximum degree of entanglement can be significantly enhanced, in a way
exhibiting a nontrivial dependence on the specifics of the modulation. Such
time-dependent driving might help to experimentally achieve entangled
mechanical systems also in situations when quantum correlations are otherwise
suppressed by thermal noise
Gently modulating optomechanical systems
No full textWe introduce a framework of optomechanical systems that are driven with a mildly amplitude-modulated light field, but that are not subject to classical feedback or squeezed input light. We find that in such a system one can achieve large degrees of squeezing of a mechanical micromirror-signifying quantum properties of optomechanical systems-without the need of any feedback and control, and within parameters reasonable in experimental settings. Entanglement dynamics is shown of states following classical quasiperiodic orbits in their first moments. We discuss the complex time dependence of the modes of a cavity-light field and a mechanical mode in phase space. Such settings give rise to certifiable quantum properties within experimental conditions feasible with present technology. © 2009 The American Physical Society
Positive wigner functions render classical simulation of quantum computation efficient
No full textWe show that quantum circuits where the initial state and all the following quantum operations can be represented by positive Wigner functions can be classically efficiently simulated. This is true both for continuous-variable as well as discrete variable systems in odd prime dimensions, two cases which will be treated on entirely the same footing. Noting the fact that Clifford and Gaussian operations preserve the positivity of the Wigner function, our result generalizes the Gottesman-Knill theorem. Our algorithm provides a way of sampling from the output distribution of a computation or a simulation, including the efficient sampling from an approximate output distribution in the case of sampling imperfections for initial states, gates, or measurements. In this sense, this work highlights the role of the positive Wigner function as separating classically efficiently simulable systems from those that are potentially universal for quantum computing and simulation, and it emphasizes the role of negativity of the Wigner function as a computational resource. © 2012 American Physical Society
Gently modulating opto-mechanical systems
No full textWe introduce a framework of optomechanical systems that are driven with a mildly amplitude-modulated light field, but that are not subject to classical feedback or squeezed input light. We find that in such a system one can achieve large degrees of squeezing of a mechanical micromirror-signifying quantum properties of optomechanical systems- without the need of any feedback and control, and within parameters reasonable in experimental settings. Entanglement dynamics is shown of states following classical quasiperiodic orbits in their first moments. We discuss the complex time dependence of the modes of a cavity-light field and a mechanical mode in phase space. Such settings give rise to certifiable quantum properties within experimental conditions feasible with present technology
Wick's theorem for matrix product states
No full textMatrix product states and their continuous analogues are variational classes of states that capture quantum many-body systems or quantum fields with low entanglement; they are at the basis of the density-matrix renormalization group method and continuous variants thereof. In this work we show that, generically, N-point functions of arbitrary operators in discrete and continuous translation invariant matrix product states are completely characterized by the corresponding two- and three-point functions. Aside from having important consequences for the structure of correlations in quantum states with low entanglement, this result provides a new way of reconstructing unknown states from correlation measurements, e.g., for one-dimensional continuous systems of cold atoms. We argue that such a relation of correlation functions may help in devising perturbative approaches to interacting theories. © 2013 American Physical Society
Positive Wigner Functions Render Classical Simulation of Quantum Computation Efficient
Full text linkWe show that quantum circuits where the initial state and all the following
quantum operations can be represented by positive Wigner functions can be
classically efficiently simulated. This is true both for continuous-variable
as well as discrete variable systems in odd prime dimensions, two cases which
will be treated on entirely the same footing. Noting the fact that Clifford
and Gaussian operations preserve the positivity of the Wigner function, our
result generalizes the Gottesman-Knill theorem. Our algorithm provides a way
of sampling from the output distribution of a computation or a simulation,
including the efficient sampling from an approximate output distribution in
the case of sampling imperfections for initial states, gates, or measurements.
In this sense, this work highlights the role of the positive Wigner function
as separating classically efficiently simulable systems from those that are
potentially universal for quantum computing and simulation, and it emphasizes
the role of negativity of the Wigner function as a computational resource
Wick’s Theorem for Matrix Product States
Full text linkMatrix product states and their continuous analogues are variational classes
of states that capture quantum many-body systems or quantum fields with low
entanglement; they are at the basis of the density-matrix renormalization
group method and continuous variants thereof. In this work we show that,
generically, N -point functions of arbitrary operators in discrete and
continuous translation invariant matrix product states are completely
characterized by the corresponding two- and three-point functions. Aside from
having important consequences for the structure of correlations in quantum
states with low entanglement, this result provides a new way of reconstructing
unknown states from correlation measurements, e.g., for one-dimensional
continuous systems of cold atoms. We argue that such a relation of correlation
functions may help in devising perturbative approaches to interacting
theories
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