5,745 research outputs found
Generation of macroscopic Schr\"odinger-cat states in qubit-oscillator systems
We propose a scheme to generate macroscopic Schr\"odinger-cat states in a
quantum harmonic oscillator (electromagnetic field or mechanical resonator)
coupled to a quantum bit (two-level system) via a conditional displacement
mechanism. By driving the qubit monochromatically, the oscillation of the qubit
state modifies the effective frequency of the driving force acting on the
oscillator, and a resonant or near-resonant driving on the oscillator can be
achieved. The displacement of the oscillator is then significantly enhanced due
to the small detuning of the driving force and can exceed that of the
zero-point fluctuation. This effect can be used to prepare quantum
superpositions of macroscopically distinct coherent states in the oscillator.
We present detailed studies on this state-generation scheme in both the closed-
and open-system cases. This approach can be implemented in various experimental
platforms, such as cavity- or circuit-QED systems, electromechanical systems,
and spin-cantilever systems.Comment: 13 pages, 11 figure
Photon blockade induced by atoms with Rydberg coupling
We study the photon blockade of two-photon scattering in a one-dimensional
waveguide, which contains two atoms coupled via the Rydberg interaction. We
obtain the analytic scattering solution of photonic wave packets with the
Laplace transform method. We examine the photon correlation by addressing the
two-photon relative wave function and the second-order correlation function in
the single- and two-photon resonance cases. It is found that, under the
single-photon resonance condition, photon bunching and antibunching can be
observed in the two-photon transmission and reflection, respectively. In
particular, the bunching and antibunching effects become stronger with the
increasing of the Rydberg coupling strength. In addition, we find a phenomenon
of bunching-antibunching transition caused by the two-photon resonance.Comment: 9 pages, 4 figure
Manipulating counter-rotating interactions in the quantum Rabi model via qubit frequency modulation
We propose a practical approach to manipulate the counter-rotating (CR)
interactions in the quantum Rabi model by introducing a sinusoidal modulation
to the transition frequency of the quantum two-level system in this model. By
choosing appropriate modulation frequency and amplitude, enhancement and
suppression of the CR interactions can be achieved in the Jaynes-Cummings
regime (including both weak- and strong-coupling cases) as well as the
ultrastrong-coupling regime. In particular, we calculate the output photon
emission of the cavity vacuum state under enhanced CR terms. Our results show
that continuous and steady photon emission from the cavity vacuum can be
observed in the Jaynes-Cummings regime as a consequence of this enhancement.
Our approach can be realized in superconducting quantum circuits.Comment: 10 pages, 9 Figure
Coherent excitation-energy transfer and quantum entanglement in a dimer
We study coherent energy transfer of a single excitation and quantum
entanglement in a dimer, which consists of a donor and an acceptor modeled by
two two-level systems. Between the donor and the acceptor, there exists a
dipole-dipole interaction, which provides the physical mechanism for coherent
energy transfer and entanglement generation. The donor and the acceptor couple
to two independent heat baths with diagonal couplings that do not dissipate the
energy of the non-coupling dimer. Special attention is paid to the effect on
single-excitation energy transfer and entanglement generation of the energy
detuning between the donor and the acceptor and the temperatures of the two
heat baths. It is found that, the probability for single-excitation energy
transfer largely depends on the energy detuning in the low temperature limit.
Concretely, the positive and negative energy detunings can increase and
decrease the probability at the steady state, respectively. In the high
temperature limit, however, the effect of the energy detuning on the
probability is neglectably small. We also find that the probability is
neglectably dependent on the bath temperature difference of the two heat baths.
In addition, it is found that quantum entanglement can be generated in the
process of coherent energy transfer. As the bath temperature increases, the
generated steady state entanglement decreases. For a given bath temperature,
the steady-state entanglement decreases with the increasing of the absolute
value of the energy detuning.Comment: 13 pages, 11 figure
Rotation Effects on Mesonic Condensations in Isospin Matter
We investigate the rotation effects on the mesonic condensation in isospin
matter . Using the two-flavor NJL effective model with a global rotation, we
demonstrate two important effects of the rotation on its phase structure: a
rotational suppression of the scalar-channel condensates, in particular the
pion condensation region; and a rotational enhancement of the rho condensation
region with vector-channel condensate. A new phase diagram for isospin matter
under rotation is mapped out on the plane where three
distinctive phases, corresponding to , , dominated regions
respectively, are separated by a second-order line at low isospin chemical
potential and a first-order line at high rotation which are further connected
at a tri-critical point.Comment: 4 pages, proceedings for Quark Matter 201
Spectral characterization of couplings in a mixed optomechanical model
We study the spectrum of single-photon emission and scattering in a mixed
optomechanical model which consists of both linear and quadratic optomechanical
interactions. The spectra are calculated based on the exact long-time solutions
of the single-photon emission and scattering processes in this system. We find
that there exist some phonon sideband peaks in the spectra and there are some
sub peaks around the phonon sideband peaks under proper parameter conditions.
The correspondence between the spectral features and the optomechanical
interactions is confirmed, and the optomechanical coupling strengths can be
inferred by analyzing the resonance peaks and dips in the spectra.Comment: 9 pages, 6 figure
Generalized Ultrastrong Optomechanics
We propose a reliable scheme to realize a generalized ultrastrong
optomechanical coupling in a two-mode cross-Kerr-type coupled system, where one
of the bosonic modes is strongly driven. The effective optomechanical
interaction takes the form of a product of the photon number operator of one
mode and the quadrature operator of the other mode. The coupling strength and
quadrature phase are both tunable via the driving field. The coupling strength
can be strongly enhanced to reach the ultrastrong-coupling regime, where the
few-photon optomechanical effects such as photon blockade and macroscopically
distinct quantum superposition become accessible. The presence of tunable
quadrature phase also enables the implementation of geometric quantum
operations. Numerical simulations show that this method works well in a wide
parameter space. We also present an analysis of the experimental implementation
of this scheme.Comment: 6 pages, 3 figures, plus supplementary materials (18 pages, 9
figures, 2 tables
Spectrometric detection of weak forces in cavity optomechanics
We propose a spectrometric method to detect a classical weak force acting
upon the moving end mirror in a cavity optomechanical system. The force changes
the equilibrium position of the end mirror, and thus the resonance frequency of
the cavity field depends on the force to be detected. As a result, the
magnitude of the force can be inferred by analyzing the single-photon emission
and scattering spectra of the optomechanical cavity. Since the emission and
scattering processes are much faster than the characteristic mechanical
dissipation, the influence of the mechanical thermal noise is negligible in
this spectrometric detection scheme. We also extent this spectrometric method
to detect a monochromatic oscillating force by utilizing an optomechanical
coupling modulated at the same frequency as the force.Comment: 16 pages, 6 figure
Ultrastrong Jaynes-Cummings Model
We propose a reliable scheme to realize the ultrastrong Jaynes-Cummings (JC)
model by simultaneously modulating the resonance frequencies of the two-level
system and the bosonic mode in the ultrastrong quantum Rabi model. We find that
in both the high- and low-frequency modulation regimes, the counter-rotating
terms can be completely suppressed without reducing the coupling strength of
the rotating-wave terms, and hence the ultrastrong JC Hamiltonian is achieved.
The ultrastrong JC interaction can not only be used to implement ultrafast
quantum operations, but also will open up a new route to the demonstration of
quantum phase transition associated with the JC Hamiltonian across the
deep-strong coupling point. Some discussions on the experimental implementation
of this scheme with circuit-QED systems are presented.Comment: 6 pages, 3 figure
Quantum simulation of a three-mode optomechanical system based on the Fredkin-type interaction
The realization of multimode optomechanical interactions in the single-photon
strong-coupling regime is a desired task in cavity optomechanics, but it
remains a challenge in realistic physical systems. In this work, we propose a
reliable scheme to simulate a three-mode optomechanical system working in the
single-photon strong-coupling regime based on the Fredkin-type interaction.
This is achieved by utilizing two strong drivings to the two exchangly-coupled
modes in the Fredkin-type coupling involving one optical mode and two
mechanical-like modes. As an application of this enhanced three-mode nonlinear
optomechanical coupling, we show how to generate entangled-cat states of the
mechanical-like modes using the conditional displacement mechanism. The quantum
coherence effects in the generated states are investigated by calculating
two-mode joint Wigner function and quantum entanglement. The influence of the
dissipation effect on the state generation is considered in the open-system
case.Comment: 11 pages, 8 figure
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