146 research outputs found
Nonclassicality of noisy quantum states
Nonclassicality conditions for an oscillator-like system interacting with a
hot thermal bath are considered. Nonclassical properties of quantum states can
be conserved up to a certain temperature threshold only. In this case,
affection of the thermal noise can be compensated via transformation of an
observable, which tests the nonclassicality (witness function). Possibilities
for experimental implementations based on unbalanced homodyning are discussed.
At the same time, we demonstrate that the scheme based on balanced homodyning
cannot be improved for noisy states with proposed technique and should be
applied directly.Comment: 15 pages, 3 figure
Free-space quantum links under diverse weather conditions
Free-space optical communication links are promising channels for
establishing secure quantum communication. Here we study the transmission of
nonclassical light through a turbulent atmospheric link under diverse weather
conditions, including rain or haze. To include these effects, the theory of
light transmission through atmospheric links in the elliptic-beam approximation
presented by Vasylyev et al. [D. Vasylyev et al., Phys. Rev. Lett. 117, 090501
(2016); arXiv:1604.01373] is further generalized.It is demonstrated, with good
agreement between theory and experiment, that low-intensity rain merely
contributes additional deterministic losses, whereas haze also introduces
additional beam deformations of the transmitted light. Based on these results,
we study theoretically the transmission of quadrature squeezing and Gaussian
entanglement under these weather conditions.Comment: 14 pages, 8 figure
Time correlations in atmospheric quantum channels
Efficient transfer of quantum information between remote parties is a crucial
challenge for quantum communication over atmospheric channels. Random
fluctuations of the channel transmittance are a major disturbing factor for its
practical implementation. We study correlations between channel transmittances
at different moments of time and focus on two transmission protocols. The first
is related to the robustness of both discrete- and continuous-variable
entanglement between time-separated light pulses, showing a possibility to
enlarge the effective dimension of the Hilbert space. The second addresses a
preselection of high-transmittance events by testing them with bright classical
pulses followed by quantum light. Our results show a high capacity of the
time-coherence resource for encoding and transferring quantum states of light
in atmospheric channels.Comment: 11 pages, 6 figures, ancillary files include Python3 code and
simulated dat
Characterization of unwanted noise in realistic cavities
The problem of the description of absorption and scattering losses in high-Q
cavities is studied. The considerations are based on quantum noise theories,
hence the unwanted noise associated with scattering and absorption is taken
into account by introduction of additional damping and noise terms in the
quantum Langevin equations and input--output relations. Completeness conditions
for the description of the cavity models obtained in this way are studied and
corresponding replacement schemes are discussed.Comment: Contribution to XI International Conference on Quantum Optics, Minsk,
Belarus, 26-31 May, 200
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