21,793 research outputs found
Extended Techniques for Feedback Control of A Single Qubit
The protection of quantum states is challenging for non-orthogonal states
especially in the presence of noises. The recent research breakthrough shows
that this difficulty can be overcome by feedback control with weak
measurements. However, the state-protection schemes proposed recently work
optimally only for special quantum states. In this paper, {by applying
different weak measurements, we extend the idea of the state-protection scheme
to protect general states.} We calculate numerically the optimal parameters and
discuss the performance of the scheme. Comparison between this extended scheme
and the earlier scheme is also presented
The Dynamical Invariant of Open Quantum System
The dynamical invariant, whose expectation value is constant, is generalized
to open quantum system. The evolution equation of dynamical invariant (the
dynamical invariant condition) is presented for Markovian dynamics. Different
with the dynamical invariant for the closed quantum system, the evolution of
the dynamical invariant for the open quantum system is no longer unitary, and
the eigenvalues of it are time-dependent. Since any hermitian operator
fulfilling dynamical invariant condition is a dynamical invariant, we propose a
sort of special dynamical invariant (decoherence free dynamical invariant) in
which a part of eigenvalues are still constant. The dynamical invariant in the
subspace spanned by the corresponding eigenstates evolves unitarily. Via the
dynamical invariant condition, the results demonstrate that this dynamical
invariant exists under the circumstances of emergence of decoherence free
subspaces
Non-Markovian Quantum Jump with Generalized Lindblad Master Equation
The Monte Carlo wave function method or the quantum trajectory/jump approach
is a powerful tool to study dissipative dynamics governed by the Markovian
master equation, in particular for high-dimensional systems and when it is
difficult to simulate directly. In this paper, we extend this method to the
non-Markovian case described by the generalized Lindblad master equation. Two
examples to illustrate the method are presented and discussed. The results show
that the method can correctly reproduce the dissipative dynamics for the
system. The difference between this method and the traditional Markovian jump
approach and the computational efficiency of this method are also discussed
Fusing atomic states via quantum Zeno dynamics
We propose a scheme for preparation of large-scale entangled states based
on the fusion mechanism via quantum Zeno dynamics. By sending two atoms
belonging to an -atom state and an -atom state, respectively,
into a vacuum cavity (or two separate cavities), we may obtain a ()-atom
state via detecting the two-atom state after interaction. The present
scheme is robust against both spontaneous emission of atoms and decay of
cavity, and the feasibility analysis indicates that it can also be realized in
experiment.Comment: 28 pages, 6 figure
Conversion of entangled states with nitrogen-vacancy centers coupled to microtoroidal resonators
We propose efficient schemes for converting three-photon, four-photon and
five-photon GHZ state to a state or Dicke state, respectively with the
nitrogen-vacancy (N-V) centers via single-photon input-output process and
cross-Kerr nonlinearities. The total success probability can be improved by
iterating the conversion process for the case of three-photon and five-photon
while it does not require iteration for converting four-photon GHZ state to a
state. The analysis of feasibility shows that our scheme is feasible for
current experimental technology.Comment: 11 pages, 6 figure
Reply to 'comment on Berry phase in a composite system'
In this reply, we show that the adiabatic theorem would break down in the
weak coupling limit, and the definition for the subsystem geometric phase is
well defined.Comment: 1 page, no figur
Quantum optical diode with semiconductor microcavities
The semiconductor diode, which acts as an electrical rectifier and allows
unidirectional electronic transports, is the key to information processing in
integrated circuits. Analogously, an optical rectifier (or diode) working at
specific target wavelengths has recently becomes a dreaming device in optical
communication and signal processing. In this paper, we propose a scheme to
realize an optical diode for photonic transport at the level of few photons.
The system consists of two spatially overlapping single-mode semiconductor
microcavities coupled via nonlinearities. The photon blockade
is predicted to take place in this system. These photon blockade effects can be
achieved by tuning the frequency of the input laser field (driving field).
Based on those blockades, we derive analytically the single- and two-photon
current in terms of zero and finite-time delayed two-order correlation
function. The results suggest that the system can serve as an single- and
two-photon quantum optical diodes which allow transmission of photons in one
direction much more efficiently than in the other.Comment: 13 pages, 6 figure
Enhanced exciton transmission by quantum-jump-based feedback
With rotating-wave approximation (RWA), we show in this paper that exciton
transmission in a one-dimensional two-level molecule chain embedded in a cavity
can be enhanced or suppressed by strong cavity-chain couplings. This exciton
transmission is closely related to the number of molecules and the distribution
of molecular exciton energy. In addition, we propose a proposal to enhance the
exciton transmission by quantum-jump-based feedback. These results may find
applications in experiments of exciton transmission in organic materials.Comment: 8 pages, 8 figure
Engineering the coupling between Majorana bound states
We study the coupling between Majorana bound states (CMBS), which is mediated
by a topologically trivial chain in the presence of pairing coupling and
long-range coupling. The results show that CMBS can be enhanced by the pairing
coupling and long-range coupling of the trivial chain. When driving the trivial
chain by periodic driving field, we deduce the analytical expressions of CMBS
in the high-frequency limit, and demonstrate that CMBS can be modulated by the
frequency and amplitude of driving field. Finally we exhibit the application of
tunable CMBS in realizing quantum logic gates.Comment: 8 pages, 8 figure
Multilevel quantum Otto heat engines with identical particles
A quantum Otto heat engine is studied with multilevel identical particles
trapped in one-dimensional box potential as working substance. The symmetrical
wave function for Bosons and the anti-symmetrical wave function for Fermions
are considered. In two-particle case, we focus on the ratios of ()
to , where and are the work done by two Bosons and Fermions
respectively, and is the work output of a single particle under the same
conditions. Due to the symmetric of the wave functions, the ratios are not
equal to . Three different regimes, low temperature regime, high temperature
regime, and intermediate temperature regime, are analyzed, and the effects of
energy level number and the differences between the two baths are calculated.
In the multiparticle case, we calculate the ratios of to , where
can be seen as the average work done by a single particle in
multiparticle heat engine.
For other working substances whose energy spectrum have the form of , the results are similar. For the case , two different
conclusions are obtained
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