39,222 research outputs found
An Efficient Algorithm for Optimizing Adaptive Quantum Metrology Processes
Quantum-enhanced metrology infers an unknown quantity with accuracy beyond
the standard quantum limit (SQL). Feedback-based metrological techniques are
promising for beating the SQL but devising the feedback procedures is difficult
and inefficient. Here we introduce an efficient self-learning
swarm-intelligence algorithm for devising feedback-based quantum metrological
procedures. Our algorithm can be trained with simulated or real-world trials
and accommodates experimental imperfections, losses, and decoherence
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
Near-Unitary Spin Squeezing in Yb
Spin squeezing can improve atomic precision measurements beyond the standard
quantum limit (SQL), and unitary spin squeezing is essential for improving
atomic clocks. We report substantial and nearly unitary spin squeezing in
Yb, an optical lattice clock atom. The collective nuclear spin of atoms is squeezed by cavity feedback, using light detuned from the
system's resonances to attain unitarity. The observed precision gain over the
SQL is limited by state readout to 6.5(4) dB, while the generated states offer
a gain of 12.9(6) dB, limited by the curvature of the Bloch sphere. Using a
squeezed state within 30% of unitarity, we demonstrate an interferometer that
improves the averaging time over the SQL by a factor of 3.7(2). In the future,
the squeezing can be simply transferred onto the optical clock transition of
Yb.Comment: 5 pages, 4 figure
SU(2)-in-SU(1,1) Nested Interferometer for Highly Sensitive, Loss-Tolerant Quantum Metrology
We present experimental and theoretical results on a new interferometer
topology that nests a SU(2) interferometer, e.g., a Mach-Zehnder or Michelson
interferometer, inside a SU(1,1) interferometer, i.e., a Mach-Zehnder
interferometer with parametric amplifiers in place of beam splitters. This
SU(2)-in-SU(1,1) nested interferometer (SISNI) simultaneously achieves high
signal-to-noise ratio (SNR), sensitivity beyond the standard quantum limit
(SQL) and tolerance to photon losses external to the interferometer, e.g., in
detectors. We implement a SISNI using parametric amplification by four-wave
mixing (FWM) in Rb vapor and a laser-fed Mach-Zehnder SU(2) interferometer. We
observe path-length sensitivity with SNR 2.2 dB beyond the SQL at power levels
(and thus SNR) 2 orders of magnitude beyond those of previous loss-tolerant
interferometers. We find experimentally the optimal FWM gains and find
agreement with a minimal quantum noise model for the FWM process. The results
suggest ways to boost the in-practice sensitivity of high-power
interferometers, e.g., gravitational wave interferometers, and may enable
high-sensitivity, quantum-enhanced interferometry at wavelengths for which
efficient detectors are not available.Comment: 6 pages + 4 of supplemental material, 5 figure
Experimental demonstration of a quantum receiver beating the standard quantum limit at the telecom wavelength
Discrimination of coherent states beyond the standard quantum limit (SQL) is
an important tasknot only for quantum information processing but also for
optical coherent communication. In orderto optimize long distance optical fiber
networks, it is of practical importance to develop a quantumreceiver beating
the SQL and approaching the quantum bound at telecom wavelength. In this
paper,we experimentally demonstrate a receiver beating the conventional SQL at
telecom wavelength. Ourreceiver is composed of a displacement operation, a
single photon counter and a real time adaptivefeedback operation. By using a
high performance single photon detector operating at the telecomwavelength, we
achieve a discrimination error beyond the SQL. The demonstration in the
telecomband provides the first step important towards quantum and classical
communication beyond theSQL using a coherent state alphabet, and we envision
that the technology can be used for long-distance quantum key distribution,
effective quantum state preparation and quantum estimation
Improving broadband displacement detection with quantum correlations
Interferometers enable ultrasensitive measurement in a wide array of
applications from gravitational wave searches to force microscopes. The role of
quantum mechanics in the metrological limits of interferometers has a rich
history, and a large number of techniques to surpass conventional limits have
been proposed. In a typical measurement configuration, the tradeoff between the
probe's shot noise (imprecision) and its quantum backaction results in what is
known as the standard quantum limit (SQL). In this work we investigate how
quantum correlations accessed by modifying the readout of the interferometer
can access physics beyond the SQL and improve displacement sensitivity.
Specifically, we use an optical cavity to probe the motion of a silicon nitride
membrane off mechanical resonance, as one would do in a broadband displacement
or force measurement, and observe sensitivity better than the SQL dictates for
our quantum efficiency. Our measurement illustrates the core idea behind a
technique known as \textit{variational readout}, in which the optical readout
quadrature is changed as a function of frequency to improve broadband
displacement detection. And more generally our result is a salient example of
how correlations can aid sensing in the presence of backaction.Comment: 17 pages, 5 figure
Beating the classical precision limit with spin-1 Dicke state of more than 10000 atoms
Interferometry is a paradigm for most precision measurements. Using
uncorrelated particles, the achievable precision for a two-mode (two-path)
interferometer is bounded by the standard quantum limit (SQL), ,
due to the discrete (quanta) nature of individual measurements. Despite being a
challenging benchmark, the two-mode SQL has been approached in a number of
systems, including the LIGO and today's best atomic clocks. Employing
multi-mode interferometry, the SQL becomes using M modes.
Higher precision can also be achieved using entangled particles such that
quantum noises from individual particles cancel out. In this work, we
demonstrate an interferometric precision of dB beyond
the three-mode SQL, using balanced spin-1 (three-mode) Dicke states containing
thousands of entangled atoms. The input quantum states are deterministically
generated by controlled quantum phase transition and exhibit close to ideal
quality. Our work shines light on the pursuit of quantum metrology beyond SQL.Comment: 11 pages, 6 figure
Entanglement-enhanced optical gyroscope
Fiber optic gyroscopes (FOG) based on the Sagnac effect are a valuable tool
in sensing and navigation and enable accurate measurements in applications
ranging from spacecraft and aircraft to self-driving vehicles such as
autonomous cars. As with any classical optical sensors, the ultimate
performance of these devices is bounded by the standard quantum limit (SQL).
Quantum-enhanced interferometry allows us to overcome this limit using
non-classical states of light. Here, we report on an entangled-photon gyroscope
that uses path-entangled NOON-states (N=2) to provide phase supersensitivity
beyond the standard-quantum-limit
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