20 research outputs found
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
Identifying entanglement using quantum "ghost" interference and imaging
We report a quantum interference and imaging experiment which quantitatively
demonstrates that Einstein-Podolsky-Rosen (EPR) type entangled two-photon
states exhibit both momentum-momentum and position-position correlations,
stronger than any classical correlation. The measurements show indeed that the
uncertainties in the sum of momenta and in the difference of positions of the
entangled two-photon satisfy both EPR inequalities D(k1+k2)<min(D(k1),D(k2))
and D(x1-x2)<min(D(x1),D(x2)). These two inequalities, together, represent a
non-classicality condition. Our measurements provide a direct way to
distinguish between quantum entanglement and classical correlation in
continuous variables for two-photons/two photons systems.Comment: We have changed Eq.(2) from one inequality to two inequalities. The
two expressions are actually consistent with each other, but the new one
represents a more stringent condition for entanglement and, in our opinion,
better explains the original idea of EPR. We have clarified this point in the
paper. 4 pages; submitted to PR
Comment on ``Dispersion-Independent High-Visibility Quantum Interference ... "
We show in this Comment that the interpretation of experimental data as well
as the theory presented in Atat\"ure et al. [Phys. Rev. Lett. 84, 618 (2000)]
are incorrect and discuss why such a scheme cannot be used to "recover"
high-visibility quantum interference.Comment: Comment on Atat\"ure et al. [Phys. Rev. Lett. 84, 618 (2000)], 2nd
revision, To appear in Phys. Rev. Lett. April, (2001
Quantum Teleportation with a Complete Bell State Measurement
We report a quantum teleportation experiment in which nonlinear interactions
are used for the Bell state measurements. The experimental results demonstrate
the working principle of irreversibly teleporting an unknown arbitrary quantum
state from one system to another distant system by disassembling into and then
later reconstructing from purely classical information and nonclassical EPR
correlations. The distinct feature of this experiment is that \emph{all} four
Bell states can be distinguished in the Bell state measurement. Teleportation
of a quantum state can thus occur with certainty in principle.Comment: 4 pages, submitted to PR
Observation of solitons in oscillating waveguide arrays
Floquet systems with periodically varying in time parameters enable
realization of unconventional topological phases that do not exist in static
systems with constant parameters and that are frequently accompanied by
appearance of novel types of the topological states. Among such Floquet systems
are the Su-Schrieffer-Heeger lattices with periodically-modulated couplings
that can support at their edges anomalous modes of topological origin
despite the fact that the lattice spends only half of the evolution period in
topologically nontrivial phase, while during other half-period it is
topologically trivial. Here, using Su-Schrieffer-Heeger arrays composed from
periodically oscillating waveguides inscribed in transparent nonlinear optical
medium, we report experimental observation of photonic anomalous modes
residing at the edge or in the corner of the one- or two-dimensional arrays,
respectively, and demonstrate a new class of topological solitons
bifurcating from such modes in the topological gap of the Floquet spectrum at
high powers. solitons reported here are strongly oscillating nonlinear
Floquet states exactly reproducing their profiles after each longitudinal
period of the structure. They can be dynamically stable in both one- and
two-dimensional oscillating waveguide arrays, the latter ones representing the
first realization of the Floquet photonic higher-order topological insulator,
while localization properties of such solitons are determined by their
power.Comment: 10 pages, 6 figures, to appear in Science Bulleti
Quantum interference by two temporally distinguishable pulses
We report a two-photon interference effect, in which the entangled photon
pairs are generated from two laser pulses well-separated in time. In a single
pump pulse case, interference effects did not occur in our experimental scheme.
However, by introducing a second pump pulse delayed in time, quantum
interference was then observed. The visibility of the interference fringes
shows dependence on the delay time between two laser pulses. The results are
explained in terms of indistinguishability of biphoton amplitudes which
originated from two temporally separated laser pulses.Comment: two-column, 4pages, submitted to PRA, minor change
Bell State Preparation using Pulsed Non-Degenerate Two-Photon Entanglement
We report a novel Bell state preparation experiment. High-purity Bell states
are prepared by using femtosecond pulse pumped \emph{nondegenerate} collinear
spontaneous parametric down-conversion. The use of femtosecond pump pulse {\em
does not} result in reduction of quantum interference visibility in our scheme
in which post-selection of amplitudes and other traditional mechanisms, such
as, using thin nonlinear crystals or narrow-band spectral filters are not used.
Another distinct feature of this scheme is that the pump, the signal, and the
idler wavelengths are all distinguishable, which is very useful for quantum
communications.Comment: 4 pages, submitted to PR