184 research outputs found
Quantum Teleportation Using Quantum Non-Demolition Technique
We propose a new scheme and protocol for quantum teleportation of a
single-mode field state, based on entanglement produced by quantum
non-demolition interaction. We show that the recently attained results in QND
technique allow to perform the teleportation in quantum regime. We also show
that applying QND coupling to squeezed fields will significantly improve the
quality of teleportation for a given degree of squeezing.Comment: 4 pages RevTeX, 2 figure
Nonlinear coherent loss for generating non-classical states
Here we discuss generation of non-classical states of bosonic mode with the
help of artificially designed loss, namely the nonlinear coherent loss. We show
how to generate superpositions of Fock states, and how it is possible to "comb"
the initial states leaving only states with certain properties in the resulting
superposition (for example, a generation of a superposition of Fock states with
odd number of particles). We discuss purity of generated states and estimate
maximal achievable generation fidelity
Afterpulsing model based on the quasi-continuous distribution of deep levels in single-photon avalanche diodes
We have performed a statistical characterization of the effect of
afterpulsing in a free-running silicon single-photon detector by measuring the
distribution of afterpulse waiting times in response to pulsed illumination and
fitting it by a sum of exponentials. We show that a high degree of goodness of
fit can be obtained for 5 exponentials, but the physical meaning of estimated
characteristic times is dubious. We show that a continuous limit of the sum of
exponentials with a uniform density between the limiting times gives excellent
fitting results in the full range of the detector response function. This means
that in certain detectors the afterpulsing is caused by a continuous band of
deep levels in the active area of the photodetector.Comment: 10 pages, 4 figure
Quantum tight-binding chains with dissipative coupling
We present a one-dimensional tight-binding chain of two-level systems coupled
only through common dissipative Markovian reservoirs. This quantum chain can
demonstrate anomalous thermodynamic behavior contradicting Fourier law.
Population dynamics of individual systems of the chain is polynomial with the
order determined by the initial state of the chain. The chain can simulate
classically hard problems, such as multi-dimensional random walks
Measuring photon-photon interactions via photon detection
The strong non-linearity plays a significant role in physics, particularly,
in designing novel quantum sources of light and matter as well as in quantum
chemistry or quantum biology. In simple systems, the photon-photon interaction
can be determined analytically. However, it becomes challenging to obtain it
for more compex systems. Therefore, we show here how to measure strong
non-linearities via allowing the sample to interact with a weakly pumped
quantized leaking optical mode. We found that the detected mean-photon number
versus pump-field frequency shows several peaks. Interestingly, the interval
between neighbour peaks equals the photon-photon interaction potential.
Furthermore, the system exhibits sub-Poissonian photon statistics, entanglement
and photon switching with less than one photon. Finally, we connect our study
with existing related experiments.Comment: 4 pages, 3 figure
Driving-dependent damping of Rabi oscillations in two-level semiconductor systems
We propose a mechanism to explain the nature of the damping of Rabi
oscillations with increasing driving-pulse area in localized semiconductor
systems, and have suggested a general approach which describes a coherently
driven two-level system interacting with a dephasing reservoir. Present
calculations show that the non-Markovian character of the reservoir leads to
the dependence of the dephasing rate on the driving-field intensity, as
observed experimentally. Moreover, we have shown that the damping of Rabi
oscillations might occur as a result of different dephasing mechanisms for both
stationary and non-stationary effects due to coupling to the environment.
Present calculated results are found in quite good agreement with available
experimental measurements
Optimal dimensionality for quantum cryptography
We perform a comparison of two protocols for generating a cryptographic key
composed from d-valued symbols: one exploiting a string of independent qubits
and another one utilizing d-level systems prepared in states belonging to d+1
mutually unbiased bases. We show that the protocol based on qubits is optimal
for quantum cryptography, since it provides higher security and higher key
generation rate.Comment: Revtex, 4 pages, 1 eps figur
Quantum state engineering via unitary transformations
We construct a Hamiltonian for the generation of arbitrary pure states of the
quantized electromagnetic field. The proposition is based upon the fact that a
unitary transformation for the generation of number states has been already
found. The general unitary transformation here obtained, would allow the use of
nonlinear interactions for the production of pure states. We discuss the
applicability of this method by giving examples of generation of simple
superposition states. We also compare our Hamiltonian with the one resulting
from the interaction of trapped ions with two laser fields.Comment: 5 pages in RevTeX, no figures, accepted for publication in Phys. Rev.
Field-emitter bound states in structured thermal reservoirs
We derive a master equation for a two-level emitter interacting with a band-gap reservoir at finite temperatures. This equation is able to capture effects of emitter-reservoir entanglement. We show that the entangled field-emitter bound state, which arises in the process of interaction, does not survive indefinitely at finite temperatures. However, such an entangled state may be effectively excited through an intensive incoherent driving.75
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