30 results found
Marques Rodrigues J, Walker BT, Dhar HS, et al., 2020, Non-stationary statistics and formation jitter in transient photon condensation, Nature Communications, Vol: 11, ISSN: 2041-1723
While equilibrium phase transitions are easily described by order parameters and free-energylandscapes, for their non-stationary counterparts these quantities are usually ill-defined. Here,we probe transient non-equilibrium dynamics of an optically pumped, dye-filled microcavity. Wequench the system to a far-from-equilibrium state and find delayed condensation close to a criticalexcitation energy, a transient equivalent of critical slowing down. Besides number fluctuations nearthe critical excitation energy, we show that transient phase transitions exhibit timing jitter in thecondensate formation. This jitter is a manifestation of the randomness associated with spontaneousemission, showing that condensation is a stochastic, rather than deterministic process. Despite thenon-equilibrium character of this phase transition, we construct an effective free-energy landscapethat describes the formation jitter and allows, in principle, its generalization to a wider class ofprocesses.
Walker BT, Rodrigues JD, Dhar HS, et al., 2020, Non-stationary statistics and formation jitter in transient photon condensation.
While equilibrium phase transitions are easily described by order parameters and free-energy landscapes, for their non-stationary counterparts these quantities are usually ill-defined. Here, we probe transient non-equilibrium dynamics of an optically pumped, dye-filled microcavity. We quench the system to a far-from-equilibrium state and find delayed condensation close to a critical excitation energy, a transient equivalent of critical slowing down. Besides number fluctuations near the critical excitation energy, we show that transient phase transitions exhibit timing jitter in the condensate formation. This jitter is a manifestation of the randomness associated with spontaneous emission, showing that condensation is a stochastic, rather than deterministic process. Despite the non-equilibrium character of this phase transition, we construct an effective free-energy landscape that describes the formation jitter and allows, in principle, its generalization to a wider class of processes.
Walker BT, Hesten HJ, Nyman RA, et al., 2019, Collective excitation profiles and the dynamics of photonic condensates, Physical Review A: Atomic, Molecular and Optical Physics, Vol: 100, Pages: 1-7, ISSN: 1050-2947
Photonic condensates are complex systems exhibiting phase transitions due to the interaction with their molecular environment. Given the macroscopic number of molecules that form a reservoir of excitations, numerical simulations are expensive, even for systems with few cavity modes. We present a systematic construction of molecular excitation profiles with a clear hierarchical ordering, such that only modes in the lowest order in the hierarchy directly affect the cavity photon dynamics. In addition to a substantial gain in computational efficiency for simulations of photon dynamics, the explicit spatial shape of the mode profiles offers a clear physical insight into the competition among the cavity modes for access to molecular excitations.
Walker BT, Hesten HJ, Dhar HS, et al., 2019, Non-critical slowing down of photonic condensation, Physical Review Letters, Vol: 123, ISSN: 0031-9007
We investigate the response of a photonic gas interacting with a reservoir ofpumped dye-molecules to quenches in the pump power. In addition to the expecteddramatic critical slowing down of the equilibration time around phasetransitions we find extremely slow equilibration even far away from phasetransitions. This non-critical slowing down can be accounted for quantitativelyby fierce competition among cavity modes for access to the molecularenvironment, and we provide a quantitative explanation for this non-criticalslowing down.
Walker BT, Flatten LC, Hesten HJ, et al., 2018, Driven-dissipative non-equilibrium Bose-Einstein condensation of less than ten photons, Nature Physics, Vol: 14, Pages: 1173-1177+, ISSN: 1745-2473
In a Bose–Einstein condensate, bosons condense in the lowest-energy mode available and exhibit high coherence. Quantum condensation is inherently a multimode phenomenon, yet understanding of the condensation transition in the macroscopic limit is hampered by the difficulty in resolving populations of individual modes and the coherences between them. Here, we report non-equilibrium Bose–Einstein condensation of 7 ± 2 photons in a sculpted dye-filled microcavity, where the extremely small particle number and large mode spacing of the condensate allow us to measure occupancies and coherences of the individual energy levels of the bosonic field. Coherence of the individual modes is found to generally increase with increasing photon number. However, at the break-down of thermal equilibrium we observe phase transitions to a multimode condensate regime wherein coherence unexpectedly decreases with increasing population, suggesting the presence of strong intermode phase or number correlations despite the absence of a direct nonlinearity. Experiments are well-matched to a detailed non-equilibrium model. We find that microlaser and Bose–Einstein statistics each describe complementary parts of our data and are limits of our model in appropriate regimes, providing elements to inform the debate on the differences between the two concepts1,2.
Nyman RA, Walker BT, 2018, Bose-Einstein condensation of photons from the thermodynamic limit to small photon numbers, Journal of Modern Optics, Vol: 65, Pages: 754-766, ISSN: 0950-0340
Photons can come to thermal equilibrium at room temperature by scattering multiple times from a fluorescent dye. By confining the light and dye in a microcavity, a minimum energy is set and the photons can then show Bose–Einstein condensation. We present here the physical principles underlying photon thermalization and condensation, and review the literature on the subject. We then explore the ‘small’ regime where very few photons are needed for condensation. We compare thermal equilibrium results to a rate-equation model of microlasers, which includes spontaneous emission into the cavity, and we note that small systems result in ambiguity in the definition of threshold.
Hesten HJ, Nyman RA, Mintert F, 2018, Decondensation in Nonequilibrium Photonic Condensates: When Less Is More, PHYSICAL REVIEW LETTERS, Vol: 120, ISSN: 0031-9007
Marelic J, Walker BT, Nyman RA, 2016, Phase-space views into dye-microcavity thermalised and condensed photons, Physical Review A, Vol: 94, ISSN: 1094-1622
We have observed momentum- and position-resolved spectra and images of the photoluminescencefrom thermalised and condensed dye-microcavity photons. The spectra yield the dispersion relationand the potential energy landscape for the photons. From this dispersion relation, below condensa-tion threshold, we nd that the e ective mass is that of a bare cavity photon not a polariton. Abovethreshold, we place an upper bound on the dimensionless two-dimensional interaction strength of~g.10
Nyman RA, Marelic J, Zajiczek LF, et al., 2016, Spatiotemporal coherence of non-equilibrium multimode photon condensates, New Journal of Physics, Vol: 18, ISSN: 1367-2630
We report on the observation of quantum coherence of Bose–Einstein condensed photons in an optically pumped, dye-filled microcavity. We find that coherence is long-range in space and time above condensation threshold, but short-range below threshold, compatible with thermal-equilibrium theory. Far above threshold, the condensate is no longer at thermal equilibrium and is fragmented over non-degenerate, spatially overlapping modes. A microscopic theory including cavity loss, molecular structure and relaxation shows that this multimode condensation is similar to multimode lasing induced by imperfect gain clamping.
Nyman R, 2016, Liquid light with a whirl, Physics, Vol: 9, ISSN: 1943-2879
Nyman RA, Marelic J, 2015, Experimental evidence for inhomogeneous pumping and energy-dependent effects in photon Bose-Einstein condensation, Physical Review A, Vol: 91, ISSN: 1094-1622
Light thermalized at room temperature in an optically pumped, dye-filled microcavity resembles a model system of noninteracting Bose-Einstein condensation in the presence of dissipation. We have experimentally investigated some of the steady-state properties of this unusual state of light and found features which do not match the available theoretical descriptions. We have seen that the critical pump power for condensation depends on the pump beam geometry, being lower for smaller pump beams. Far below threshold, both intracavity photon number and thermalized photon cloud size depend on pump beam size, with optimal coupling when the pump beam matches the thermalized cloud size. We also note that the critical pump power for condensation depends on the cavity cutoff wavelength and longitudinal mode number, which suggests that energy-dependent thermalization and loss mechanisms are important.
Nyman RA, Kohnen M, 2015, Temporal and spatiotemporal correlation functions for trapped Bose gases, Physical Review A, Vol: 91, ISSN: 1094-1622
Density correlations unambiguously reveal the quantum nature of matter. Here, we study correlations between measurements of density in cold-atom clouds at different times at one position, and also at two separated positions. We take into account the effects of finite-size and -duration measurements made by light beams passing through the atom cloud. We specialize to the case of Bose gases in harmonic traps above critical temperature, for weakly perturbative measurements. For overlapping measurement regions, shot-noise correlations revive after a trap oscillation period. For nonoverlapping regions, bosonic correlations dominate at long times, and propagate at finite speeds. Finally, we give a realistic measurement protocol for performing such experiments.
Nyman RA, Szymanska MH, 2014, Interactions in dye-microcavity photon condensates and the prospects for their observation, PHYSICAL REVIEW A, Vol: 89, ISSN: 1050-2947
Nyman RA, Scheel S, Hinds EA, 2011, Prospects for using integrated atom-photon junctions for quantum information processing, QUANTUM INFORMATION PROCESSING, Vol: 10, Pages: 941-953, ISSN: 1570-0755
Kohnen M, Petrov PG, Nyman RA, et al., 2011, Minimally destructive detection of magnetically trapped atoms using frequency-synthesized light, NEW JOURNAL OF PHYSICS, Vol: 13, ISSN: 1367-2630
Photonic chips that integrate optical elements on a single device can process vast amounts of information rapidly. A new branch of this technology involves coupling light to cold atoms or Bose–Einstein condensates, the quantum nature of which provides a basis for new information-processing methods. The use of optical waveguides gives the light a small cross-section, making coupling to atoms efficient. In this Letter, we present the first waveguide chip designed to address a Bose–Einstein condensate along a row of independent junctions, which are separated by only 10 µm and have large atom–photon coupling. We describe a fully integrated, scalable design, and demonstrate 11 junctions working as intended, using a low-density cold atom cloud with as little as one atom on average in any one junction. The device suggests new possibilities for engineering quantum states of matter and light on a microscopic scale.
Varoquaux G, Nyman RA, Geiger R, et al., 2009, How to estimate the differential acceleration in a two-species atom interferometer to test the equivalence principle, NEW JOURNAL OF PHYSICS, Vol: 11, ISSN: 1367-2630
Clement J-F, Brantut J-P, Robert-de-Saint-Vincent M, et al., 2009, All-optical runaway evaporation to Bose-Einstein condensation, PHYSICAL REVIEW A, Vol: 79, ISSN: 1050-2947
Brantut JP, Clement JF, de Saint Vincent MR, et al., 2008, Light-shift tomography in an optical-dipole trap for neutral atoms, PHYSICAL REVIEW A, Vol: 78, ISSN: 1050-2947
Varoquaux G, Zahzam N, Chaibi W, et al., 2007, I.C.E.: An Ultra-Cold Atom Source for Long-Baseline Interferometric Inertial Sensors in Reduced Gravity, http://uk.arxiv.org/abs/0705.2922, Rencontres de Moriond Gravitational Waves and Experimental Gravity
Nyman RA, Varoquaux G, Lienhart F, et al., 2006, ICE: a transportable atomic inertial sensor for test in microgravity, Publisher: SPRINGER HEIDELBERG, Pages: 673-681, ISSN: 0946-2171
Nyman RA, Varoquaux G, Villier B, et al., 2006, Tapered-amplified antireflection-coated laser diodes for potassium and rubidium atomic-physics experiments, REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 77, ISSN: 0034-6748
Bowley RM, Buu O, Nyman RA, 2004, The effect of the demagnetizing field on the NMR spectra for liquids enclosed in a cylinder, JOURNAL OF LOW TEMPERATURE PHYSICS, Vol: 137, Pages: 1-26, ISSN: 0022-2291
Nyman RA, Buu OVL, Clubb D, et al., 2003, A realistic model of spin-transport in dilute He-3 in He-4 in a finite geometry, 23rd International Conference on Low Temperature Physics (LT23), Publisher: ELSEVIER SCIENCE BV, Pages: 183-184, ISSN: 0921-4526
Buu O, Nyman R, Clubb D, et al., 2002, Transverse spin diffusion in He-3-He-4 mixtures - Part II, JOURNAL OF LOW TEMPERATURE PHYSICS, Vol: 128, Pages: 143-162, ISSN: 0022-2291
Buu O, Clubb D, Nyman R, et al., 2002, Transverse spin diffusion in He-3-He-4 mixtures - Part I, JOURNAL OF LOW TEMPERATURE PHYSICS, Vol: 128, Pages: 123-142, ISSN: 0022-2291
Rodrigues JD, Dhar HS, Walker BT, et al., Unsupervised Learning of the Fuzzy Phases of Small Photonic Condensates
Phase transitions, while ubiquitous in nature, are formally defined only inthe thermodynamic limit. While criticality is well approximated in largesystems, large relative fluctuations in systems made up of only a few particlesstrongly hinder our ability to identify and characterize different phases ofmatter. Here, we demonstrate that unsupervised learning and fuzzy logic permitthe detection of the otherwise inaccessible and subtle phase structure of smallphysical systems, in a data-driven and model-free approach. We thus introducethe concept of fuzzy phases and, in particular, construct the fuzzy phasediagram of a photonic condensate made up of only a few photons. The notion ofthermodynamic phases and phase transitions is therefore generalized into therealm of finite, and particularly small, physical systems.
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