8,585 research outputs found
Quantum state testing beyond the polarizing regime and quantum triangular discrimination
The complexity class Quantum Statistical Zero-Knowledge ()
captures computational difficulties of the time-bounded quantum state testing
problem with respect to the trace distance, known as the Quantum State
Distinguishability Problem (QSDP) introduced by Watrous (FOCS 2002). However,
QSDP is in merely within the constant polarizing regime,
similar to its classical counterpart shown by Sahai and Vadhan (JACM 2003) due
to the polarization lemma (error reduction for SDP).
Recently, Berman, Degwekar, Rothblum, and Vasudevan (TCC 2019) extended the
containment for SDP beyond the polarizing regime via the
time-bounded distribution testing problems with respect to the triangular
discrimination and the Jensen-Shannon divergence. Our work introduces proper
quantum analogs for these problems by defining quantum counterparts for
triangular discrimination. We investigate whether the quantum analogs behave
similarly to their classical counterparts and examine the limitations of
existing approaches to polarization regarding quantum distances. These new
-complete problems improve containments for QSDP
beyond the polarizing regime and establish a simple -hardness
for the quantum entropy difference problem (QEDP) defined by Ben-Aroya,
Schwartz, and Ta-Shma (ToC 2010). Furthermore, we prove that QSDP with some
exponentially small errors is in , while the same problem without
error is in .Comment: 31 pages. v3: added a simple QSZK-hardness proof for QEDP, updated a
correct version of Theorem 5.1(2), and improved presentation. v2: minor
change
Cold heteromolecular dipolar collisions
We present the first experimental observation of cold collisions between two
different species of neutral polar molecules, each prepared in a single
internal quantum state. Combining for the first time the techniques of Stark
deceleration, magnetic trapping, and cryogenic buffer gas cooling allows the
enhancement of molecular interaction time by 10. This has enabled an
absolute measurement of the total trap loss cross sections between OH and
ND at a mean collision energy of 3.6 cm (5 K). Due to the dipolar
interaction, the total cross section increases upon application of an external
polarizing electric field. Cross sections computed from \emph{ab initio}
potential energy surfaces are in excellent agreement with the measured value at
zero external electric field. The theory presented here represents the first
such analysis of collisions between a radical and a closed-shell
polyatomic molecule.Comment: 7 pages, 5 figure
Cold heteromolecular dipolar collisions
We present the first experimental observation of cold collisions between two
different species of neutral polar molecules, each prepared in a single
internal quantum state. Combining for the first time the techniques of Stark
deceleration, magnetic trapping, and cryogenic buffer gas cooling allows the
enhancement of molecular interaction time by 10. This has enabled an
absolute measurement of the total trap loss cross sections between OH and
ND at a mean collision energy of 3.6 cm (5 K). Due to the dipolar
interaction, the total cross section increases upon application of an external
polarizing electric field. Cross sections computed from \emph{ab initio}
potential energy surfaces are in excellent agreement with the measured value at
zero external electric field. The theory presented here represents the first
such analysis of collisions between a radical and a closed-shell
polyatomic molecule.Comment: 7 pages, 5 figure
Reversible compression of an optical piston through Kramers dynamics
We study the reversible crossover between stable and bistable phases of an
over-damped Brownian bead inside an optical piston. The interaction potentials
are solved developing a method based on Kramers' theory that exploits the
statistical properties of the stochastic motion of the bead. We evaluate
precisely the energy balance of the crossover. We show that the deformation of
the optical potentials induced by the compression of the piston is related to a
production of heat which measures the non-adiabatic character of the crossover.
This reveals how specific thermodynamic processes can be designed and
controlled with a high level of precision by tailoring the optical landscapes
of the piston.Comment: 9 pages, 9 figure
Photonic qubits, qutrits and ququads accurately prepared and delivered on demand
Reliable encoding of information in quantum systems is crucial to all
approaches to quantum information processing or communication. This applies in
particular to photons used in linear optics quantum computing (LOQC), which is
scalable provided a deterministic single-photon emission and preparation is
available. Here, we show that narrowband photons deterministically emitted from
an atom-cavity system fulfill these requirements. Within their 500 ns coherence
time, we demonstrate a subdivision into d time bins of various amplitudes and
phases, which we use for encoding arbitrary qu-d-its. The latter is done
deterministically with a fidelity >95% for qubits, verified using a newly
developed time-resolved quantum-homodyne method.Comment: 5 pages, 4 figure
Strong Optomechanical Squeezing of Light
We create squeezed light by exploiting the quantum nature of the mechanical
interaction between laser light and a membrane mechanical resonator embedded in
an optical cavity. The radiation pressure shot noise (fluctuating optical force
from quantum laser amplitude noise) induces resonator motion well above that of
thermally driven motion. This motion imprints a phase shift on the laser light,
hence correlating the amplitude and phase noise, a consequence of which is
optical squeezing. We experimentally demonstrate strong and continuous
optomechanical squeezing of 1.7 +/- 0.2 dB below the shot noise level. The peak
level of squeezing measured near the mechanical resonance is well described by
a model whose parameters are independently calibrated and that includes thermal
motion of the membrane with no other classical noise sources.Comment: 12 pages, 8 figure
Properties of a Variable-delay Polarization Modulator
We investigate the polarization modulation properties of a variable-delay
polarization modulator (VPM). The VPM modulates polarization via a variable
separation between a polarizing grid and a parallel mirror. We find that in the
limit where the wavelength is much larger than the diameter of the metal wires
that comprise the grid, the phase delay derived from the geometric separation
between the mirror and the grid is sufficient to characterize the device.
However, outside of this range, additional parameters describing the polarizing
grid geometry must be included to fully characterize the modulator response. In
this paper, we report test results of a VPM at wavelengths of 350 microns and 3
mm. Electromagnetic simulations of wire grid polarizers were performed and are
summarized using a simple circuit model that incorporates the loss and
polarization properties of the device.Comment: 25 pages, 10 figures, accepted by Applied Optic
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