1,727 research outputs found
Observing quantum state diffusion by heterodyne detection of fluorescence
A qubit can relax by fluorescence, which prompts the release of a photon into
its electromagnetic environment. By counting the emitted photons, discrete
quantum jumps of the qubit state can be observed. The succession of states
occupied by the qubit in a single experiment, its quantum trajectory, depends
in fact on the kind of detector. How are the quantum trajectories modified if
one measures continuously the amplitude of the fluorescence field instead?
Using a superconducting parametric amplifier, we have performed heterodyne
detection of the fluorescence of a superconducting qubit. For each realization
of the measurement record, we can reconstruct a different quantum trajectory
for the qubit. The observed evolution obeys quantum state diffusion, which is
characteristic of quantum measurements subject to zero point fluctuations.
Independent projective measurements of the qubit at various times provide a
quantitative validation of the reconstructed trajectories. By exploring the
statistics of quantum trajectories, we demonstrate that the qubit states span a
deterministic surface in the Bloch sphere at each time in the evolution.
Additionally, we show that when monitoring fluorescence, coherent
superpositions are generated during the decay from excited to ground state.
Counterintuitively, measuring light emitted during relaxation can give rise to
trajectories with increased excitation probability.Comment: Supplementary material can be found in the ancillary sectio
On the central quadric ansatz: integrable models and Painleve reductions
It was observed by Tod and later by Dunajski and Tod that the Boyer-Finley
(BF) and the dispersionless Kadomtsev-Petviashvili (dKP) equations possess
solutions whose level surfaces are central quadrics in the space of independent
variables (the so-called central quadric ansatz). It was demonstrated that
generic solutions of this type are described by Painleve equations PIII and
PII, respectively. The aim of our paper is threefold:
-- Based on the method of hydrodynamic reductions, we classify integrable
models possessing the central quadric ansatz. This leads to the five canonical
forms (including BF and dKP).
-- Applying the central quadric ansatz to each of the five canonical forms,
we obtain all Painleve equations PI - PVI, with PVI corresponding to the
generic case of our classification.
-- We argue that solutions coming from the central quadric ansatz constitute
a subclass of two-phase solutions provided by the method of hydrodynamic
reductions.Comment: 12 page
Using Spontaneous Emission of a Qubit as a Resource for Feedback Control
Persistent control of a transmon qubit is performed by a feedback protocol
based on continuous heterodyne measurement of its fluorescence. By driving the
qubit and cavity with microwave signals whose amplitudes depend linearly on the
instantaneous values of the quadratures of the measured fluorescence field, we
show that it is possible to stabilize permanently the qubit in any targeted
state. Using a Josephson mixer as a phase-preserving amplifier, it was possible
to reach a total measurement efficiency =35%, leading to a maximum of 59%
of excitation and 44% of coherence for the stabilized states. The experiment
demonstrates multiple-input multiple-output analog Markovian feedback in the
quantum regime.Comment: Supplementary material can be found as an ancillary objec
Generating Entangled Microwave Radiation Over Two Transmission Lines
Using a superconducting circuit, the Josephson mixer, we demonstrate the
first experimental realization of spatially separated two-mode squeezed states
of microwave light. Driven by a pump tone, a first Josephson mixer generates,
out of quantum vacuum, a pair of entangled fields at different frequencies on
separate transmission lines. A second mixer, driven by a -phase shifted
copy of the first pump tone, recombines and disentangles the two fields. The
resulting output noise level is measured to be lower than for vacuum state at
the input of the second mixer, an unambiguous proof of entanglement. Moreover,
the output noise level provides a direct, quantitative measure of entanglement,
leading here to the demonstration of 6 Mebit.s (Mega entangled bits per
second) generated by the first mixer.Comment: 5 pages, 4 figures. Supplementary Information can be found here as an
ancillary fil
Eyesys vs. Mastervue RGP fitting study
Background: Videokeratography has recently emerged on the scene as a powerful tool in understanding the dimensions of the human cornea. Computer software exists that can generate rigid gas permeable contact lens fitting parameters based on a topography reading.
Methods: This study will assess the fitting performance, both subjectively and objectively, of two Placido based topography systems: Humphrey MasterVue and EyeSys Corneal Analysis System. Twenty four subjects were fit and dispensed a pair of lenses: one eye\u27s lens generated by each computer. Lenses were rated by both the examiners and the patients using standard rating scales at the time of the dispensing visit.
Results: Overall the Master Vue lenses were preferred by 57% of the subjects, the EyeSys 19%, and 24% had no preference. Objectively we assessed that the MasterVue lenses physiologically out performed the EyeSys lenses a majority of the time.
Conclusions: Generally, the MasterVue software did a better job than the EyeSys program of matching base curve and overall diameter dimensions with the measured cornea. However, there is significant room for improvement in both systems to become clinically useful
Widely tunable, non-degenerate three-wave mixing microwave device operating near the quantum limit
We present the first experimental realization of a widely frequency tunable,
non-degenerate three-wave mixing device for quantum signals at GHz frequency.
It is based on a new superconducting building-block consisting of a ring of
four Josephson junctions shunted by a cross of four linear inductances. The
phase configuration of the ring remains unique over a wide range of magnetic
fluxes threading the loop. It is thus possible to vary the inductance of the
ring with flux while retaining a strong, dissipation-free, and noiseless
non-linearity. The device has been operated in amplifier mode and its noise
performance has been evaluated by using the noise spectrum emitted by a voltage
biased tunnel junction at finite frequency as a test signal. The unprecedented
accuracy with which the crossover between zero-point-fluctuations and shot
noise has been measured provides an upper-bound for the noise and dissipation
intrinsic to the device.Comment: Accepted for Physical Review Letters. Supplementary material can be
found in the source packag
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