647 research outputs found
Phase space tweezers for tailoring cavity fields by quantum Zeno dynamics
We discuss an implementation of Quantum Zeno Dynamics in a Cavity Quantum
Electrodynamics experiment. By performing repeated unitary operations on atoms
coupled to the field, we restrict the field evolution in chosen subspaces of
the total Hilbert space. This procedure leads to promising methods for
tailoring non-classical states. We propose to realize `tweezers' picking a
coherent field at a point in phase space and moving it towards an arbitrary
final position without affecting other non-overlapping coherent components.
These effects could be observed with a state-of-the-art apparatus
Qubit-oscillator system under ultrastrong coupling and extreme driving
We introduce an approach to studying a driven qubit-oscillator system in the
ultrastrong coupling regime, where the ratio between coupling
strength and oscillator frequency approaches unity or goes beyond, and
simultaneously for driving strengths much bigger than the qubit energy
splitting (extreme driving). Both qubit-oscillator coupling and external
driving lead to a dressing of the qubit tunneling matrix element of different
nature: the former can be used to suppress selectively certain oscillator modes
in the spectrum, while the latter can bring the qubit's dynamics to a
standstill at short times (coherent destruction of tunneling) even in the case
of ultrastrong coupling.Comment: 4+ pages, 5 figures (published version
Generation of Superposition States and Charge-Qubit Relaxation Probing in a Circuit
We demonstrate how a superposition of coherent states can be generated for a
microwave field inside a coplanar transmission line coupled to a single
superconducting charge qubit, with the addition of a single classical magnetic
pulse for chirping of the qubit transition frequency. We show how the qubit
dephasing induces decoherence on the field superposition state, and how it can
be probed by the qubit charge detection. The character of the charge qubit
relaxation process itself is imprinted in the field state decoherence profile.Comment: 6 pages, 4 figure
Entanglement signature in the mode structure of a single photon
It is shown that entanglement, which is a quantum correlation property of at
least two subsystems, is imprinted in the mode structure of a single photon.
The photon, which is emitted by two coupled cavities, carries the information
on the concurrence of the two intracavity fields. This can be useful for
recording the entanglement dynamics of two cavity fields and for entanglement
transfer.Comment: 4 pages, 3 figure
Optomechanical trapping and cooling of partially transparent mirrors
We consider the radiative trapping and cooling of a partially transmitting
mirror suspended inside an optical cavity, generalizing the case of a perfectly
reflecting mirror previously considered [M. Bhattacharya and P. Meystre, Phys.
Rev. Lett. \textbf{99}, 073601 (2007)]. This configuration was recently used in
an experiment to cool a nanometers-thick membrane [Thompson \textit{et al.},
arXiv:0707.1724v2, 2007]. The self-consistent cavity field modes of this system
depend strongly on the position of the middle mirror, leading to important
qualitative differences in the radiation pressure effects: in one case, the
situation is similar that of a perfectly reflecting middle mirror, with only
minor quantitative modifications. In addition, we also identify a range of
mirror positions for which the radiation-mirror coupling becomes purely
dispersive and the back-action effects that usually lead to cooling are absent,
although the mirror can still be optically trapped. The existence of these two
regimes leads us to propose a bichromatic scheme that optimizes the cooling and
trapping of partially transmissive mirrors.Comment: Submitted to Phys.Rev.
Coherently controlled entanglement generation in a binary Bose-Einstein condensate
Considering a two-component Bose-Einstein condensate in a double-well
potential, a method to generate a Bell state consisting of two spatially
separated condensates is suggested. For repulsive interactions, the required
tunnelling control is achieved numerically by varying the amplitude of a
sinusoidal potential difference between the wells. Both numerical and
analytical calculations reveal the emergence of a highly entangled mesoscopic
state.Comment: 6 pages, 6 figures, epl2.cl
Quantum state tomography using a single apparatus
The density matrix of a two-level system (spin, atom) is usually determined
by measuring the three non-commuting components of the Pauli vector. This
density matrix can also be obtained via the measurement data of two commuting
variables, using a single apparatus. This is done by coupling the two-level
system to a mode of radiation field, where the atom-field interaction is
described with the Jaynes--Cummings model. The mode starts its evolution from a
known coherent state. The unknown initial state of the atom is found by
measuring two commuting observables: the population difference of the atom and
the photon number of the field. We discuss the advantages of this setup and its
possible applications.Comment: 7 pages, 8 figure, Phys. Rev.
Observation of Entanglement Between Itinerant Microwave Photons and a Superconducting Qubit
A localized qubit entangled with a propagating quantum field is well suited
to study non-local aspects of quantum mechanics and may also provide a channel
to communicate between spatially separated nodes in a quantum network. Here, we
report the on demand generation and characterization of Bell-type entangled
states between a superconducting qubit and propagating microwave fields
composed of zero, one and two-photon Fock states. Using low noise linear
amplification and efficient data acquisition we extract all relevant
correlations between the qubit and the photon states and demonstrate
entanglement with high fidelity.Comment: 5 pages, 3 figure
Non-Local Quantum Gates: a Cavity-Quantum-Electro-Dynamics implementation
The problems related to the management of large quantum registers could be
handled in the context of distributed quantum computation: unitary non-local
transformations among spatially separated local processors are realized
performing local unitary transformations and exchanging classical
communication. In this paper, we propose a scheme for the implementation of
universal non-local quantum gates such as a controlled-\gate{NOT} (\cnot)
and a controlled-quantum phase gate (\gate{CQPG}). The system we have chosen
for their physical implementation is a Cavity-Quantum-Electro-Dynamics (CQED)
system formed by two spatially separated microwave cavities and two trapped
Rydberg atoms. We describe the procedures to follow for the realization of each
step necessary to perform a specific non-local operation.Comment: 12 pages, 5 figures, RevTeX; extensively revised versio
Quantum Zeno dynamics of a field in a cavity
We analyze the quantum Zeno dynamics that takes place when a field stored in
a cavity undergoes frequent interactions with atoms. We show that repeated
measurements or unitary operations performed on the atoms probing the field
state confine the evolution to tailored subspaces of the total Hilbert space.
This confinement leads to non-trivial field evolutions and to the generation of
interesting non-classical states, including mesoscopic field state
superpositions. We elucidate the main features of the quantum Zeno mechanism in
the context of a state-of-the-art cavity quantum electrodynamics experiment. A
plethora of effects is investigated, from state manipulations by phase space
tweezers to nearly arbitrary state synthesis. We analyze in details the
practical implementation of this dynamics and assess its robustness by
numerical simulations including realistic experimental imperfections. We
comment on the various perspectives opened by this proposal
- …