Photon Interferometry Research Articles

Non-Hermitian Sensing in the Absence of Exceptional Points.

Open systems possess unique potentials in high-precision sensing, yet the majority of previous studies rely on the spectral singularities known as "exceptional points." Here, we theoretically propose and experimentally demonstrate universal non-Hermitian sensing in the absence of exceptional points. The scheme makes use of the intrinsic sensitivity of a non-Hermitian probe to weak external fields, which can be understood as the direct consequence of non-Hermiticity. We confirm the basic mechanism by simulating the sensor-field dynamics using photon interferometry, and, as a concrete example, demonstrate the enhanced sensing of signals encoded in the setting angle of a wave plate. While the sensitivity of the probe is ultimately limited by the measurement noise, we find the non-Hermitian sensor showing superior performance under background noises that cannot be suppressed through repetitive measurements. Our experiment opens the avenue of enhanced sensing without exceptional points, complementing existing efforts aimed at harnessing the unique features of open systems.

Measuring axion gradients with photon interferometry

We propose a novel search technique for axions with a CP-violating monopole coupling g˜Q to bulk Standard Model charges Q∈{B,L,B−L}. Gradients in the static axion field configurations sourced by matter induce achromatic circular photon birefringence via the axion-photon coupling gϕγ. Circularly polarized light fed into an optical or (open) radio-frequency (RF) Fabry-Pérot (FP) cavity develops a phase shift that accumulates up to the cavity finesse: the fixed axion spatial gradient prevents a cancellation known to occur for an axion dark-matter search. The relative phase shift between two FP cavities fed with opposite circular polarizations can be detected interferometrically. This time-independent signal can be modulated up to nonzero frequency by altering the cavity orientations with respect to the field gradient. Multiwavelength co-metrology techniques can be used to address chromatic measurement systematics and noise sources. With Earth as the axion source, we project reach beyond current constraints on the product of couplings g˜Qgϕγ for axion masses mϕ≲10−5 eV. If shot-noise-limited sensitivity can be achieved, an experiment using high-finesse RF FP cavities could reach a factor of ∼105 into new parameter space for g˜Qgϕγ for masses mϕ≲4×10−11 eV. Published by the American Physical Society 2024

Quantum-limited determination of refractive index difference by means of entanglement

Shaping single-mode operation in high-power fibers requires a precise knowledge of the gain-medium optical properties. This requires precise measurements of the refractive index differences (Δn) between the core and the cladding of the fiber. We exploit a quantum optical method based on low-coherence Hong-Ou-Mandel interferometry to perform practical measurements of the refractive index difference using broadband energy-time entangled photons. The precision enhancement reached with this method is benchmarked with a classical method based on single photon interferometry. We show in classical regime an improvement by an order of magnitude of the precision compared to already reported classical methods. Strikingly, in the quantum regime, we demonstrate an extra factor of 4 on the precision enhancement, exhibiting a state-of-the-art Δn precision of 6 × 10−7. This work sets the quantum photonics metrology as a powerful characterization tool that should enable a faster and reliable design of materials dedicated to light amplification.

Investigations of Molecular Optical Properties Using Quantum Light and Hong-Ou-Mandel Interferometry.

Entangled photon pairs have been used for molecular spectroscopy in the form of entangled two-photon absorption and in quantum interferometry for precise measurements of light source properties and time delays. We present an experiment that combines molecular spectroscopy and quantum interferometry by utilizing the correlations of entangled photons in a Hong-Ou-Mandel (HOM) interferometer to study molecular properties. We find that the HOM signal is sensitive to the presence of a resonant organic sample placed in one arm of the interferometer, and the resulting signal contains information pertaining to the light-matter interaction. We can extract the dephasing time of the coherent response induced by the excitation on a femtosecond time scale. A dephasing time of 102 fs is obtained, which is relatively short compared to times found with similar methods and considering line width broadening and the instrument entanglement time As the measurement is done with coincidence counts as opposed to simply intensity, it is unaffected by even-order dispersion effects, and because interactions with the molecular state affect the photon correlation, the observed measurement contains only these effects and no other classical losses. The experiments are accompanied by theory that predicts the observed temporal shift and captures the entangled photon joint spectral amplitude and the molecule's transmission in the coincidence counting rate. Thus, we present a proof-of-concept experimental method based of entangled photon interferometry that can be used to characterize optical properties in organic molecules and can in the future be expanded on for more complex spectroscopic studies of nonlinear optical properties.

Quantum Locality in Game Strategy

Game theory is a well established branch of mathematics whose formalism has a vast range of applications from the social sciences, biology, to economics. Motivated by quantum information science, there has been a leap in the formulation of novel game strategies that lead to new (quantum Nash) equilibrium points whereby players in some classical games are always outperformed if sharing and processing joint information ruled by the laws of quantum physics is allowed. We show that, for a bipartite non zero-sum game, input local quantum correlations, and separable states in particular, suffice to achieve an advantage over any strategy that uses classical resources, thus dispensing with quantum nonlocality, entanglement, or even discord between the players’ input states. This highlights the remarkable key role played by pure quantum coherence at powering some protocols. Finally, we propose an experiment that uses separable states and basic photon interferometry to demonstrate the locally-correlated quantum advantage.

A novel interferometric mass spectrometry concept

A novel mass spectrometry concept is presented here which is based on interferometric principle using a newly discovered matter wave on the macro-scale for a charged particle moving in a magnetic field. The wave length of the matter wave involves the mass of the ions, whose features can be used for mass discrimination in the same manner as the photon interferometry is used for discriminating the different wave lengths of light. The concept involves injecting the ions of a given sample consisting of isotopes of a certain element to be discriminated along a uniform magnetic field and varying the magnetic field which sweeps through the various interference peaks. The different masses are then identified through the location of their interference peaks which are mass dependent because of the mass dependence of the associated macro-scale matter wave lengths.

Evolution of collectivity as a signal of quark gluon plasma formation in heavy ion collisions

A measurement for studying the mass dependence of the dilepton interferometry in relativistic heavy-ion collision experiments as a tool to characterize the quark-gluon phase is proposed. In calculations involving dileptons, we show that the mass dependence of radii extracted from the virtual photon (dilepton) interferometry provide access to the development of collective flow with time. It is argued that the non-monotonic variation of HBT radii with invariant mass of the lepton pairs signals the formation of quark gluon plasma in heavy ion collisions. Our proposal of experimentally measuring the ratio, $R_{\mathrm out}/R_{\mathrm side}$ for dileptons can be used to estimate the average life times of the partonic as well as the hadronic phases.

Improving the performance of quantum key distribution apparatus

Results of active phase tracking system deployment for quantum communication are presented. The system allows high-visibility single photon interferometry over 100 km of standard optical fibre. Single photon detector optimization is performed and the estimates for long-distance quantum key distribution with heralded single photon source are presented.

Review of HBT or Bose-Einstein correlations in high energy heavy ion collisions

A brief review is given on the discovery and the first five decades of the Hanbury Brown–Twiss effect and its generalized applications in high energy nuclear and particle physics, that includes a meta-review. Interesting and inspiring new directions are also highlighted, including for example source imaging, lepton and photon interferometry, non-Gaussian shape analysis as well as many other new directions. Existing models are compared to two-particle correlation measurements and the so-called RHIC HBT puzzle is resolved. Evidence for a (directional) Hubble flow is presented and the conclusion is confirmed by a successful description of the pseudorapidity dependence of the elliptic flow as measured in Au+Au collisions by the PHOBOS Collaboration.

Intensity interferometry of thermal photons from relativistic heavy-ion collisions

Intensity interferometry of thermal photons, having transverse momenta $k_T \approx $ 0.1 -- 2.0 GeV, produced in relativistic collision of heavy nuclei is studied. It is seen to provide an accurate information about the temporal and spatial structure of the interacting system. The source dimensions and their $k_T$ dependence revealed by the photon interferometry, display a richness not seen in pion interferometry. We attribute this to difference in the source functions, the fact that photons come out from every stage of the collision and from every point in the system, and the fact that the rate of production of photons is different for the quark-gluon plasma, which dominates the early hot stage, and the hadronic matter which populates the last phase of the collision dynamics. The usefulness of this procedure is demonstrated by an application to collision of lead nuclei at the CERN SPS. Prediction for the transverse momentum dependence of the sizes for SPS, RHIC, and LHC energies are given.

Measurement of Geometric Phase for Mixed States Using Single Photon Interferometry

Geometric phase may enable inherently fault-tolerant quantum computation. However, due to potential decoherence effects, it is important to understand how such phases arise for mixed input states. We report the first experiment to measure mixed-state geometric phases in optics, using a Mach-Zehnder interferometer, and polarization mixed states that are produced in two different ways: decohering pure states with birefringent elements; and producing a nonmaximally entangled state of two photons and tracing over one of them, a form of remote state preparation.

Mesoscopic Interferometers for Electron Waves

Mesoscopic interferometers are electronic analogues of optical interferometers, with “quantum point contacts” playing the role of optical beam splitters. Mesoscopic analogues of two-slit, Mach-Zehnder and Fabry-Perot interferometers have been built. A fundamental difference between electron and photon interferometry is that electron interferometry is nonlocal.

Photon Interferometry ofAu+AuCollisions at the BNL Relativistic Heavy-Ion Collider

We calculate the two-body correlation function of direct photons produced in central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at the Relativistic Heavy-Ion Collider. Our calculation includes contributions from the early preequilibrium phase in which photons are produced via hard parton scatterings as well as radiation of photons from a thermalized quark-gluon plasma and the subsequent expanding hadron gas. We find that high energy photon interferometry provides a faithful probe of the details of the space-time evolution and of the early reaction stages of the system.

Photon interferometry and size of the hot zone in relativistic heavy ion collisions

The parameters obtained from the theoretical analysis of the single photon spectra observed by the WA98 collaboration at SPS energies have been used to evaluate the two photon correlation functions. The single photon spectra and the two photon correlations at RHIC energies have also been evaluated, taking into account the effects of the possible spectral change of hadrons in a thermal bath. We find that the ratio $R_{side}/R_{out} \sim 1$ for SPS and $R_{side}/R_{out} <1$ for RHIC energy.

Photon interferometry of quark-gluon dynamics reexamined.

The Bose-Einstein correlations of photons emitted from a longitudinally expanding system of excited matter produced in ultrarelativistic heavy ion collisions are studied. Two effects found in recent calculations---that the correlation function in longitudinal direction exhibits oscillations, and that it takes values below unity---are demonstrated to be numerical artefacts and/or the results of inappropriate approximations. Thus, the general quantum statistical bounds for the two particle correlation function of a chaotic source with Gaussian fluctuations are confirmed. Two different expressions for the two-photon inclusive distribution are considered. Depending on which of the two expressions is used in the calculation, the width of the correlation function may vary by as much as 30%.

Fidelity of photon interferometry for recording the evolution of a nascent quark-gluon plasma.

The fidelity of two-photon intensity interferometry for reflecting the dynamics of nascnt quark-gluon plasma formed in a high energy nucleus-nucleus collision is examined. A (3 + 1)-dimensional expansion of the plasma as well as a (1 + 1)-dimensional expansion according to Bjorken hydrodynamics, both with a first order phase transition, are considered. The correlation of high transverse-momentum photons is shown to be a precision tool for the investigation of the space-time evolution of the high density QCD plasma. In particular, the longitudinal correlation function, which depicts the development of the system, is seen to have its origin in two sources: one corresponding to the early plasma phase and the second to the later stages. This aspect may help identify thermal photons according to their time of birth during evolution.

History of quark-gluon plasma evolution from photon interferometry.

Two-photon intensity interferometry is used to probe the dynamics of quarks and gluons in a high-energy nucleus-nucleus collision. A (1+1)-dimensional expansion of the plasma according to Bjorken hydrodynamics as well as a (3+1)-dimensional expansion, both with a first-order phase transition, are considered. The correlation of high transverse-momentum photons is sensitive to the details of the space-time evolution of the high density QCD plasma. The so-called ``longitudinal'' and ``outward'' correlations are found to be dramatically affected by the transverse expansion of the system.

Single-particle trajectories and interferences in quantum mechanics

In this paper some topics concerning the possibility of describing phenomena of quantum interference in terms of individual particle spacetime trajectories are reviewed. We focus our attention, on the one hand, on the recent experimental advances in neutron and photon interferometry and, on the other hand, on a theoretical analysis of the description of these experiments allowed by stochastic mechanics. It is argued that, even if no conclusive argument is yet at hand in both the theoretical and the experimental fields, the researches of the last 10 years now seem to favor Einstein's and de Broglie's realistic spacetime description and interpretation of quantum mechanics.

Hanbury Brown/Twiss correlations for expanding hadron and quark-gluon matter

Some basic theoretical and experimental aspects of the interferometry method for expanding sources are discussed. We summarize the pion interferometry results for sources of a hydrodynamical type, analyze the features of the correlation method for a deflagrating mixed qg-h phase and the photon interferometry of an expanding quark-gluon plasma.

Thin-film phonon interferometry

Thin-film phonon interferences can be used to build fast phonon spectrometers. The analogy and the differences to thin-film photon interferometry and to Fourier spectroscopy are worked out and related experiments with photons are described. Multiplebeam interferograms are observed in growing cryogenic films using coherent 24-GHz phonons.