1,987 research outputs found
Minimalist design of a robust real-time quantum random number generator
We present a simple and robust construction of a real-time quantum random
number generator (QRNG). Our minimalist approach ensures stable operation of
the device as well as its simple and straightforward hardware implementation as
a stand-alone module. As a source of randomness the device uses measurements of
time intervals between clicks of a single-photon detector. The obtained raw
sequence is then filtered and processed by a deterministic randomness
extractor, which is realized as a look-up table. This enables high speed
on-the-fly processing without the need of extensive computations. The overall
performance of the device is around 1 random bit per detector click, resulting
in 1.2 Mbit/s generation rate in our implementation
Quantum phase slips in the presence of finite-range disorder
To study the effect of disorder on quantum phase slips (QPS) in
superconducting wires, we consider the plasmon-only model where disorder can be
incorporated into a first-principles instanton calculation. We consider weak
but general finite-range disorder and compute the formfactor in the QPS rate
associated with momentum transfer. We find that the system maps onto
dissipative quantum mechanics, with the dissipative coefficient controlled by
the wave (plasmon) impedance Z of the wire and with a superconductor-insulator
transition at Z=6.5 kOhm. We speculate that the system will remain in this
universality class after resistive effects at the QPS core are taken into
account.Comment: 4 pages, as accepted at Phys. Rev. Letter
Width of the longitudinal magnon in the vicinity of the O(3) quantum critical point
We consider a three-dimensional quantum antiferromagnet in the vicinity of a
quantum critical point separating the magnetically ordered and the magnetically
disordered phases. A specific example is TlCuCl where the quantum phase
transition can be driven by hydrostatic pressure and/or by external magnetic
field. As expected two transverse and one longitudinal magnetic excitation have
been observed in the pressure driven magnetically ordered phase. According to
the experimental data, the longitudinal magnon has a substantial width, which
has not been understood and has remained a puzzle. In the present work, we
explain the mechanism for the width, calculate the width and relate value of
the width with parameters of the Bose condensate of magnons observed in the
same compound. The method of an effective quantum field theory is employed in
the work.Comment: 6 pages, 3 figure
Anisotropically high entanglement of biphotons generated in spontaneous parametric down conversion
We show that the wave packet of a biphoton generated via spontaneous
parametric down conversion is strongly anisotropic. Its anisotropic features
manifest themselves very clearly in comparison of measurements performed in two
different schemes: when the detector scanning plane is perpendicular or
parallel to the plane containing the crystal optical axis and the laser axis.
The first of these two schemes is traditional whereas the second one gives rise
to such unexpected new results as anomalously strong narrowing of the biphoton
wave packet measured in the coincidence scheme and very high degree of
entanglement. The results are predicted theoretically and confirmed
experimentally
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