78 research outputs found
Advances in quantum machine learning
Here we discuss advances in the field of quantum machine learning. The
following document offers a hybrid discussion; both reviewing the field as it
is currently, and suggesting directions for further research. We include both
algorithms and experimental implementations in the discussion. The field's
outlook is generally positive, showing significant promise. However, we believe
there are appreciable hurdles to overcome before one can claim that it is a
primary application of quantum computation.Comment: 38 pages, 17 Figure
Maximizing precision in saturation-limited absorption measurements
Quantum fluctuations in the intensity of an optical probe is noise which
limits measurement precision in absorption spectroscopy. Increased probe power
can offer greater precision, however, this strategy is often constrained by
sample saturation. Here, we analyse measurement precision for a generalised
absorption model in which we account for saturation and explore its effect on
both classical and quantum probe performance. We present a classical
probe-sample optimisation strategy to maximise precision and find that optimal
probe powers always fall within the saturation regime. We apply our
optimisation strategy to two examples, high-precision Doppler broadened
thermometry and an absorption spectroscopy measurement of Chlorophyll A. We
derive a limit on the maximum precision gained from using a non-classical probe
and find a strategy capable of saturating this bound. We evaluate
amplitude-squeezed light as a viable experimental probe state and find it
capable of providing precision that reaches to within > 85% of the ultimate
quantum limit with currently available technology.Comment: 12 pages and 5 figure
Passive, broadband and low-frequency suppression of laser amplitude noise to the shot-noise limit using hollow-core fibre
We use hollow-core fibre to preserve the spectrum and temporal profile of
picosecond laser pulses in CBD to suppress 2.6 dB of amplitude noise at MHz
noise frequencies, to within 0.01 dB of the shot-noise limit. We provide an
enhanced version of the CBD scheme that concatenates circuits to suppress over
multiple frequencies and over broad frequency ranges --- we perform a first
demonstration that reduces total excess amplitude noise, between 2 - 6 MHz, by
85%. These demonstrations enable passive, broad-band, all-guided fibre laser
technology operating at the shot-noise limit.Comment: 8 pages, 8 figure
Quantum Absorbance Estimation and the Beer-Lambert Law
The utility of transmission measurement has made it a target for quantum
enhanced measurement strategies. Here we find if the length of an absorbing
object is a controllable variable, then via the Beer-Lambert law, classical
strategies can be optimised to reach within 83% of the absolute quantum limit.
Our analysis includes experimental losses, detector noise, and input states
with arbitrary photon statistics. We derive optimal operating conditions for
both classical and quantum sources, and observe experimental agreement with
theory using Fock and thermal states.Comment: 12 pages, 8 figure
9~GHz measurement of squeezed light by interfacing silicon photonics and integrated electronics
Photonic quantum technology can be enhanced by monolithic fabrication of both
the underpinning quantum hardware and the corresponding electronics for
classical readout and control. Together, this enables miniaturisation and
mass-manufacture of small quantum devices---such as quantum communication
nodes, quantum sensors and sources of randomness---and promises the precision
and scale of fabrication required to assemble useful quantum computers. Here we
combine CMOS compatible silicon and germanium-on-silicon nano-photonics with
silicon-germanium integrated amplification electronics to improve performance
of on-chip homodyne detection of quantum light. We observe a 3 dB bandwidth of
1.7 GHz, shot-noise limited performance beyond 9 GHz and minaturise the
required footprint to 0.84 mm. We use the device to observe quantum squeezed
light, from 100 MHz to 9 GHz, generated in a lithium niobate waveguide. This
demonstrates that an all-integrated approach yields faster homodyne detectors
for quantum technology than has been achieved to-date and opens the way to
full-stack integration of photonic quantum devices.Comment: Nat. Photonics (2020
Methane emissions from oil and gas platforms in the North Sea
Since 1850 the concentration of atmospheric methane (CH4), a potent greenhouse gas, has more than doubled. Recent studies suggest that emission inventories may be missing sources and underestimating emissions. To investigate whether offshore oil and gas platforms leak CH4 during normal operation, we measured CH4 mole fractions around eight oil and gas production platforms in the North Sea which were neither flaring gas nor offloading oil. We use the measurements from summer 2017, along with meteorological data, in a Gaussian plume model to estimate CH4 emissions from each platform. We find CH4 mole fractions of between 11 and 370 ppb above background concentrations downwind of the platforms measured, corresponding to a median CH4 emission of 6.8 g CH4 s−1 for each platform, with a range of 2.9 to 22.3 g CH4 s−1. When matched to production records, during our measurements individual platforms lost between 0.04 % and 1.4 % of gas produced with a median loss of 0.23 %. When the measured platforms are considered collectively (i.e. the sum of platforms' emission fluxes weighted by the sum of the platforms' production), we estimate the CH4 loss to be 0.19 % of gas production. These estimates are substantially higher than the emissions most recently reported to the National Atmospheric Emission Inventory (NAEI) for total CH4 loss from United Kingdom platforms in the North Sea. The NAEI reports CH4 losses from the offshore oil and gas platforms we measured to be 0.13 % of gas production, with most of their emissions coming from gas flaring and offshore oil loading, neither of which was taking place at the time of our measurements. All oil and gas platforms we observed were found to leak CH4 during normal operation, and much of this leakage has not been included in UK emission inventories. Further research is required to accurately determine total CH4 leakage from all offshore oil and gas operations and to properly include the leakage in national and international emission inventories
Quantum Optical Metrology of Correlated Phase and Loss
Optical absorption measurements characterize a wide variety of systems from atomic gases to in vivo diagnostics of living organisms. Here we study the potential of nonclassical techniques to reduce statistical noise below the shot-noise limit in absorption measurements with concomitant phase shifts imparted by a sample. We consider both cases where there is a known relationship between absorption and a phase shift, and where this relationship is unknown. For each case we derive the fundamental limit and provide a practical strategy to reduce statistical noise. Furthermore, we find an intuitive correspondence between measurements of absorption and of lossy phase shifts, which both show the same analytical form for precision enhancement for bright states. Our results demonstrate that nonclassical techniques can aid real-world tasks with present-day laboratory techniques
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