22,643 research outputs found
Fourier Phase Retrieval with a Single Mask by Douglas-Rachford Algorithm
Douglas-Rachford (DR) algorithm is analyzed for Fourier phase retrieval with
a single random phase mask. Local, geometric convergence to a unique fixed
point is proved with numerical demonstration of global convergence
DART-ID increases single-cell proteome coverage.
Analysis by liquid chromatography and tandem mass spectrometry (LC-MS/MS) can identify and quantify thousands of proteins in microgram-level samples, such as those comprised of thousands of cells. This process, however, remains challenging for smaller samples, such as the proteomes of single mammalian cells, because reduced protein levels reduce the number of confidently sequenced peptides. To alleviate this reduction, we developed Data-driven Alignment of Retention Times for IDentification (DART-ID). DART-ID implements principled Bayesian frameworks for global retention time (RT) alignment and for incorporating RT estimates towards improved confidence estimates of peptide-spectrum-matches. When applied to bulk or to single-cell samples, DART-ID increased the number of data points by 30-50% at 1% FDR, and thus decreased missing data. Benchmarks indicate excellent quantification of peptides upgraded by DART-ID and support their utility for quantitative analysis, such as identifying cell types and cell-type specific proteins. The additional datapoints provided by DART-ID boost the statistical power and double the number of proteins identified as differentially abundant in monocytes and T-cells. DART-ID can be applied to diverse experimental designs and is freely available at http://dart-id.slavovlab.net
Observing and Verifying the Quantum Trajectory of a Mechanical Resonator
Continuous weak measurement allows localizing open quantum systems in state
space, and tracing out their quantum trajectory as they evolve in time.
Efficient quantum measurement schemes have previously enabled recording quantum
trajectories of microwave photon and qubit states. We apply these concepts to a
macroscopic mechanical resonator, and follow the quantum trajectory of its
motional state conditioned on a continuous optical measurement record. Starting
with a thermal mixture, we eventually obtain coherent states of 78%
purity--comparable to a displaced thermal state of occupation 0.14. We
introduce a retrodictive measurement protocol to directly verify state purity
along the trajectory, and furthermore observe state collapse and decoherence.
This opens the door to measurement-based creation of advanced quantum states,
and potential tests of gravitational decoherence models.Comment: 20 pages, 4 figure
Measurement-based quantum control of mechanical motion
Controlling a quantum system based on the observation of its dynamics is
inevitably complicated by the backaction of the measurement process. Efficient
measurements, however, maximize the amount of information gained per
disturbance incurred. Real-time feedback then enables both canceling the
measurement's backaction and controlling the evolution of the quantum state.
While such measurement-based quantum control has been demonstrated in the clean
settings of cavity and circuit quantum electrodynamics, its application to
motional degrees of freedom has remained elusive. Here we show
measurement-based quantum control of the motion of a millimetre-sized membrane
resonator. An optomechanical transducer resolves the zero-point motion of the
soft-clamped resonator in a fraction of its millisecond coherence time, with an
overall measurement efficiency close to unity. We use this position record to
feedback-cool a resonator mode to its quantum ground state (residual thermal
occupation n = 0.29 +- 0.03), 9 dB below the quantum backaction limit of
sideband cooling, and six orders of magnitude below the equilibrium occupation
of its thermal environment. This realizes a long-standing goal in the field,
and adds position and momentum to the degrees of freedom amenable to
measurement-based quantum control, with potential applications in quantum
information processing and gravitational wave detectors.Comment: New version with corrected detection efficiency as determined with a
NIST-calibrated photodiode, added references and revised structure. Main
conclusions are identical. 41 pages, 18 figure
Continuous Force and Displacement Measurement Below the Standard Quantum Limit
Quantum mechanics dictates that the precision of physical measurements must
be subject to certain constraints. In the case of inteferometric displacement
measurements, these restrictions impose a 'standard quantum limit' (SQL), which
optimally balances the precision of a measurement with its unwanted backaction.
To go beyond this limit, one must devise more sophisticated measurement
techniques, which either 'evade' the backaction of the measurement, or achieve
clever cancellation of the unwanted noise at the detector. In the half-century
since the SQL was established, systems ranging from LIGO to ultracold atoms and
nanomechanical devices have pushed displacement measurements towards this
limit, and a variety of sub-SQL techniques have been tested in
proof-of-principle experiments. However, to-date, no experimental system has
successfully demonstrated an interferometric displacement measurement with
sensitivity (including all relevant noise sources: thermal, backaction, and
imprecision) below the SQL. Here, we exploit strong quantum correlations in an
ultracoherent optomechanical system to demonstrate off-resonant force and
displacement sensitivity reaching 1.5dB below the SQL. This achieves an
outstanding goal in mechanical quantum sensing, and further enhances the
prospects of using such devices for state-of-the-art force sensing
applications.Comment: 18 pages, 7 figure
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