728 research outputs found
Steady state entanglement of two superconducting qubits engineered by dissipation
We present a scheme for the dissipative preparation of an entangled steady
state of two superconducting qubits in a circuit QED setup. Combining resonator
photon loss, a dissipative process already present in the setup, with an
effective two-photon microwave drive, we engineer an effective decay mechanism
which prepares a maximally entangled state of the two qubits. This state is
then maintained as the steady state of the driven, dissipative evolution. The
performance of the dissipative state preparation protocol is studied
analytically and verified numerically. In view of the experimental
implementation of the presented scheme we investigate the effects of potential
experimental imperfections and show that our scheme is robust to small
deviations in the parameters. We find that high fidelities with the target
state can be achieved both with state-of-the-art 3D, as well as with the more
commonly used 2D transmons. The promising results of our study thus open a
route for the demonstration of an entangled steady state in circuit QED.Comment: 12 pages, 5 figures; close to published versio
Non-perturbative Dynamical Casimir Effect in Optomechanical Systems: Vacuum Casimir-Rabi Splittings
We study the dynamical Casimir effect using a fully quantum-mechanical
description of both the cavity field and the oscillating mirror. We do not
linearize the dynamics, nor do we adopt any parametric or perturbative
approximation. By numerically diagonalizing the full optomechanical
Hamiltonian, we show that the resonant generation of photons from the vacuum is
determined by a ladder of mirror-field {\em vacuum Rabi splittings}. We find
that vacuum emission can originate from the free evolution of an initial pure
mechanical excited state, in analogy with the spontaneous emission from excited
atoms. By considering a coherent drive of the mirror, using a master-equation
approach to take losses into account, we are able to study the dynamical
Casimir effect for optomechanical coupling strengths ranging from weak to
ultrastrong. We find that a resonant production of photons out of the vacuum
can be observed even for mechanical frequencies lower than the cavity-mode
frequency. Since high mechanical frequencies, which are hard to achieve
experimentally, were thought to be imperative for realizing the dynamical
Casimir effect, this result removes one of the major obstacles for the
observation of this long-sought effect. We also find that the dynamical Casimir
effect can create entanglement between the oscillating mirror and the radiation
produced by its motion in the vacuum field, and that vacuum Casimir-Rabi
oscillations can occur.Comment: 30 pages, 8 figure
Deterministic atom-light quantum interface
The notion of an atom-light quantum interface has been developed in the past
decade, to a large extent due to demands within the new field of quantum
information processing and communication. A promising type of such interface
using large atomic ensembles has emerged in the past several years. In this
article we review this area of research with a special emphasis on
deterministic high fidelity quantum information protocols. Two recent
experiments, entanglement of distant atomic objects and quantum memory for
light are described in detail.Comment: 50 pages (bookstyle) 15 graphs, to be published in "Advances in
Atomic, Molecular, and Optical Physics" Vol. 54. (2006)(Some of the graphs
here have lower resolution than in the version to be published
Quantum sensing
"Quantum sensing" describes the use of a quantum system, quantum properties
or quantum phenomena to perform a measurement of a physical quantity.
Historical examples of quantum sensors include magnetometers based on
superconducting quantum interference devices and atomic vapors, or atomic
clocks. More recently, quantum sensing has become a distinct and rapidly
growing branch of research within the area of quantum science and technology,
with the most common platforms being spin qubits, trapped ions and flux qubits.
The field is expected to provide new opportunities - especially with regard to
high sensitivity and precision - in applied physics and other areas of science.
In this review, we provide an introduction to the basic principles, methods and
concepts of quantum sensing from the viewpoint of the interested
experimentalist.Comment: 45 pages, 13 figures. Submitted to Rev. Mod. Phy
Quantum Memories. A Review based on the European Integrated Project "Qubit Applications (QAP)"
We perform a review of various approaches to the implementation of quantum
memories, with an emphasis on activities within the quantum memory sub-project
of the EU Integrated Project "Qubit Applications". We begin with a brief
overview over different applications for quantum memories and different types
of quantum memories. We discuss the most important criteria for assessing
quantum memory performance and the most important physical requirements. Then
we review the different approaches represented in "Qubit Applications" in some
detail. They include solid-state atomic ensembles, NV centers, quantum dots,
single atoms, atomic gases and optical phonons in diamond. We compare the
different approaches using the discussed criteria.Comment: 22 pages, 12 figure
Enantioselective switch on radiations of dissipative chiral molecules
Enantiodetection is an important and challenging task across natural science.
Nowadays, some chiroptical methods of enantiodetection based on
decoherence-free cyclic three-level models of chiral molecules can reach the
ultimate limit of the enantioselectivities in the molecular responses. They are
thus more efficient than traditional chiroptical methods. However, decoherence
is inevitable and can severely reduce enantioselectivities in these advanced
chiroptical methods, so they only work well in the weak decoherence region.
Here, we propose an enantioselective switch on the radiation of dissipative
chiral molecules and develop a novel chiroptical method of enantiodetection
working well in all decoherence regions. In our scheme, radiation is turned on
for the selected enantiomer and simultaneously turned off for its mirror image
by designing the electromagnetic fields well based on dissipative cyclic
three-level models. The enantiomeric excess of a chiral mixture is determined
by comparing its emissions in two cases, where the radiations of two
enantiomers are turned off respectively. The corresponding enantioselectivities
reach the ultimate limit in all decoherence regions, offering our scheme
advantages over other chiroptical methods in enantiodetection. Our work
potentially constitutes the starting point for developing more efficient
chiroptical techniques for enantiodection in all decoherence regions
Dissipative dynamics of circuit-QED in the mesoscopic regime
We investigate the behavior of a circuit QED device when the resonator is
initially populated with a mesoscopic coherent field. The strong coupling
between the cavity and the qubit produces an entangled state involving
mesoscopic quasi-pointer states with respect to cavity dissipation. The overlap
of the associated field components results in collapse and revivals for the
Rabi oscillation. Although qubit relaxation and dephasing do not preserve these
states, a simple analytical description of the dissipative dynamics of the
circuit QED device including cavity relaxation as well as qubit dissipation is
obtained from the Monte-Carlo approach. Explicit predictions for the
spontaneous and induced Rabi oscillation signals are derived and sucessfully
compared with exact calculations. We show that these interesting effects could
be observed with a 10 photon field in forthcoming circuit QED experiments.Comment: 10 figures, 1 tabl
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