Photonic Maxwell's demon

We report an experimental realisation of Maxwell's demon in a photonic setup. We show that a measurement at the single-photon level followed by a feed-forward operation allows the extraction of work from intense thermal light into an electric circuit. The interpretation of the experiment stimulates the derivation of a new equality relating work extraction to information acquired by measurement. We derive a bound using this relation and show that it is in agreement with the experimental results. Our work puts forward photonic systems as a platform for experiments related to information in thermodynamics.Comment: 8 pages, 3 figure

Joint estimation of phase and phase diffusion for quantum metrology

Phase estimation, at the heart of many quantum metrology and communication schemes, can be strongly affected by noise, whose amplitude may not be known, or might be subject to drift. Here, we investigate the joint estimation of a phase shift and the amplitude of phase diffusion, at the quantum limit. For several relevant instances, this multiparameter estimation problem can be effectively reshaped as a two-dimensional Hilbert space model, encompassing the description of an interferometer phase probed with relevant quantum states -- split single-photons, coherent states or N00N states. For these cases, we obtain a trade-off bound on the statistical variances for the joint estimation of phase and phase diffusion, as well as optimum measurement schemes. We use this bound to quantify the effectiveness of an actual experimental setup for joint parameter estimation for polarimetry. We conclude by discussing the form of the trade-off relations for more general states and measurements.Comment: Published in Nature Communications. Supplementary Information available at http://www.nature.com/ncomms/2014/140404/ncomms4532/extref/ncomms4532-s1.pd

Theory of high-gain twin-beam generation in waveguides: From Maxwell's equations to efficient simulation

We provide an efficient method for the calculation of high-gain, twin-beam generation in waveguides derived from a canonical treatment of Maxwell's equations. Equations of motion are derived that naturally accommodate photon generation via spontaneous parametric down-conversion (SPDC) or spontaneous four-wave mixing (SFWM), and also include the effects of both self-phase modulation (SPM) of the pump, and of cross-phase modulation(XPM) of the twin beams by the pump. The equations we solve involve fields that evolve in space and are labelled by a frequency. We provide a proof that these fields satisfy bonafide commutation relations, and that in the distant past and future they reduce to standard time-evolving Heisenberg operators. Having solved for the input-output relations of these Heisenberg operators we also show how to construct the ket describing the quantum state of the twin-beams. Finally, we consider the example of high-gain SPDC in a waveguide with a flat nonlinearity profile, for which our approach provides an explicit solution that requires only a single matrix exponentiation

Weak measurements and the joint estimation of phase and phase diffusion

Weak measurements offer the possibility of tuning the information acquired on a system, hence the imposed disturbance. This suggests that it could be a useful tool for multiparameter estimation, when two parameters cannot be measured simultaneously at the quantum limit. Here we discuss their use for phase estimation in the presence of phase diffusion in the context of polarimetry, a scenario that is conveniently cast in terms of a two-level quantum system in many relevant cases

Maxwell’s Demon in Photonic Systems

Photons are massless, noninteracting particles, and thermodynamics seems to be completely inappropriate in their description. Here we present two examples of the opposite: connecting thermodynamics with information through Maxwell’s Demon provides interesting insight on properties of light fields. This does not amount to directly applying thermodynamics to photons, but rather helps to obtain tools and concepts from thermodynamics to manipulate and evaluate the information content of light. The examples presented here pinpoint some of the challenges that arise when putting a thought experiment into practice and provide new insights into the relation between thermodynamic work and information