4,925 research outputs found
Deterministic CNOT gate and entanglement swapping for photonic qubits using a quantum-dot spin in a double-sided optical microcavity
We propose a deterministic and scalable scheme to construct a two-qubit
controlled-NOT (CNOT) gate and realize entanglement swapping between photonic
qubits using a quantum-dot (QD) spin in a double-sided optical microcavity. The
scheme is based on spin selective photon reflection from the cavity and can be
achieved in a nondestructive and heralded way. We assess the feasibility of the
scheme and show that the scheme can work in both the weak coupling and the
strong coupling regimes. The scheme opens promising perspectives for
long-distance photonic quantum communication and distributed quantum
information processing.Comment: 18 pages, 5 figures; to appear in Physics Letters
Evolving hypernetwork model based on WeChat user relations
Based on the theory of hypernetwork and WeChat online social relations, the
paper proposes an evolving hypernetwork model with the competitiveness and the
age of nodes. In the model, nodes arrive at the system in accordance with
Poisson process and are gradual aging. We analyze the model by using a Poisson
process theory and a continuous technique, and give a characteristic equation
of hyperdegrees. We obtain the stationary average hyperdegree distribution of
the hypernetwork by the characteristic equation. The numerical simulations of
the models agree with the analytical results well. It is expected that our work
may give help to the study of WeChat information transmission dynamics and
mobile e-commerce.Comment: 14 pages, in Chinese, 5 figure
Optically controlled phase gate and teleportation of a controlled-NOT gate for spin qubits in quantum dot-microcavity coupled system
Assisted with linear optical manipulation, single photon, entangled photon
pairs, photon measurement, and classical communication, a scheme for two-spin
qubits phase gate and teleportation of a CNOT gate between two electron spins
from acting on local qubits to acting on remote qubits using quantum dots in
optical microcavities is proposed. The scheme is based on spin selective photon
reflection from the cavity and is achieved in a deterministic way by the
sequential detection of photons and the single-qubit rotations of a single
electron spin in a self-assembled GaAs/InAs quantum dot. The feasibility of the
scheme is assessed showing that high average fidelities of the gates are
achievable in the weak-coupling regime when the side leakage and cavity loss
are low. The scheme opens promising perspectives for long-distance quantum
communication, distributed quantum computation, and constructing remote quantum
information processing networks.Comment: 14 pages, 5 figures, to appear in Physical Review
Robust entanglement between a movable mirror and atomic ensemble and entanglement transfer in coupled optomechanical system
We propose a scheme for the creation of robust entanglement between a movable
mirror and atomic ensemble at the macroscopic level in coupled optomechanical
system. In experimentally accessible parameter regimes, we show that critical
temperature of the bipartite continuous variable entanglement in our scheme can
be raised from previous 24 K [Vitali {\it et al.}, Phys. Rev. Lett.
\textbf{98}, 030405 (2007)] and 20 K [Genes {\it et al.}, Phys. Rev. A
\textbf{77}, 050307(R) (2008)] to 32 K. We also investigate the entanglement
transfer based on this coupled system. The scheme can be used for the
realization of quantum memories for continuous variable quantum information
processing and quantum-limited displacement measurements.Comment: 18 pages, 4 figure
Modulation of entanglement between two oscillators separated in space with an optical parametric amplifier
We propose a scheme to modulate the entanglement between two oscillators
separated in space via the squeezing cavity field generated by the optical
parametric amplifier instead of injecting the squeezing field directly with the
assistance of Coulomb interaction. We show that the Coulomb interaction between
the oscillators is the essential reason for the existence of entanglement. Due
to the gain of the optical parametric amplifier and the phase of the pump
driving the optical parametric amplifier can simultaneously modulate the
squeezing cavity field, the radiation pressure interaction between the cavity
field and the oscillator is modulated accordingly. We find that there is
competing effect between the radiation pressure interaction and the Coulomb
interaction for the oscillator which these two interactions act on
simultaneously. Therefore, the modulation of entanglement can be achieved with
the assistance of Coulomb interaction. The results of numerical simulation show
that the present scheme has stronger robustness against the temperature of
environment compared with previous schemes in experimentally feasible regimes.Comment: 19 pages, 5 figure
Steady-state mechanical squeezing in a double-cavity optomechanical system
We study the physical properties of double-cavity optomechanical system in
which the mechanical resonator interacts with one of the coupled cavities and
another cavity is used as an auxiliary cavity. The model can be expected to
achieve the strong optomechanical coupling strength and overcome the
optomechanical cavity decay, simultaneously. Through the coherent auxiliary
cavity interferences, the steady-state squeezing of mechanical resonator can be
generated in highly unresolved sideband regime. The validity of the scheme is
assessed by numerical simulation and theoretical analysis of the steady-state
variance of the mechanical displacement quadrature. The scheme provides a
platform for the mechanical squeezing beyond the resolved sideband limit and
addresses the restricted experimental bounds at present.Comment: 15 pages, 5 figures. arXiv admin note: substantial text overlap with
arXiv:1512.0653
Steady-state mechanical squeezing in a hybrid atom-optomechanical system with a highly dissipative cavity
Quantum squeezing of mechanical resonator is important for studying the
macroscopic quantum effects and the precision metrology of weak forces. Here we
give a theoretical study of a hybrid atom-optomechanical system in which the
steady-state squeezing of the mechanical resonator can be generated via the
mechanical nonlinearity and cavity cooling process. The validity of the scheme
is assessed by simulating the steady-state variance of the mechanical
displacement quadrature numerically. The scheme is robust against dissipation
of the optical cavity, and the steady-state squeezing can be effectively
generated in a highly dissipative cavity
Direct conversion of a three-atom W state to a Greenberger-Horne-Zeilinger state in spatially separated cavities
State conversion between Greenberger-Horne-Zeilinger (GHZ) state and W state
is an open challenging problem because they cannot be converted to each other
only by local operations and classical communication. Here we propose a cavity
quantum electrodynamics method based on interference of polarized photons
emitted by the atoms trapped in spatially separated optical cavities that can
convert a three-atom W state to a GHZ state. We calculate the success
probability and fidelity of the converted GHZ state when the cavity decay,
atomic spontaneous decay, and photon leakage of the cavities are taken into
account for a practical system, which shows that the proposed scheme is
feasible and within the reach of current experimental technology.Comment: 12pages, 4 figures; to appear in Journal of Physics B: Atomic,
Molecular and Optical Physic
Multi-qubit non-adiabatic holonomic controlled quantum gates in decoherence-free subspaces
Non-adiabatic holonomic quantum gate in decoherence-free subspaces is of
greatly practical importance due to its built-in fault tolerance, coherence
stabilization virtues, and short run-time. Here we propose some compact schemes
to implement two- and three-qubit controlled unitary quantum gates and Fredkin
gate. For the controlled unitary quantum gates, the unitary operator acting on
the target qubit is an arbitrary single-qubit gate operation. The controlled
quantum gates can be directly implemented using non-adiabatic holonomy in
decoherence-free subspaces and the required resource for the decoherence-free
subspace encoding is minimal by using only two neighboring physical qubits
undergoing collective dephasing to encode a logical qubit.Comment: 12 pages, 0 figure
Spontaneous PT symmetry breaking in non-Hermitian coupled cavities array
We study the effects of the position of the passive and active cavities on
the spontaneous parity-time (PT) symmetry breaking behavior in non-Hermitian
coupled cavities array model. We analyze and discuss the energy eigenvalue
spectrums and PT symmetry in the topologically trivial and nontrivial regimes
under three different cases in detail, i.e., the passive and active cavities
are located at, respectively, the two end positions, the second and penultimate
positions, and each position in coupled cavities array. The odevity of the
number of cavities is further considered to check the effects of the
non-Hermitian terms applied on the PT symmetric and asymmetric systems. We find
that the position of the passive and active cavities has remarkable impacts on
the spontaneous PT symmetry breaking behavior, and in each case the system
exhibits distinguishable and novel spontaneous PT symmetry breaking
characteristic, respectively. The effects of the non-Hermitian terms on the
symmetric and asymmetric systems due to the odevity are
comparatively different in the first case while qualitatively same in the
second case
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