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Register a new userQuantum hydrodynamics of a single particle
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Added by
Daniel Gustavo Suarez Forero
Publication date
2019
fields
Physics
and research's language is
English
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Semiconductor devices are strong competitors in the race for the development of quantum com-putational systems. In this work, we interface two semiconductor building blocks of different di-mensionality and with complementary properties: (1) a quantum dot hosting a single exciton andacting as a nearly ideal single-photon emitter and (2) a quantum well in a 2D microcavity sustain-ing polaritons, which are known for their strong interactions and unique hydrodynamics propertiesincluding ultrafast real-time monitoring of their propagation and phase-mapping. In the presentexperiment we can thus observe how the injected single particles propagate and evolve inside themicrocavity, giving rise to hydrodynamics features typical of macroscopic systems despite their in-trinsic genuine quantum nature. In the presence of a structural defect, we observe the celebratedquantum interference of a single particle that produces fringes reminiscent of a wave propagation.While this behaviour could be theoretically expected, our imaging of such an interference pattern,together with a measurement of antibunching, constitutes the first demonstration of spatial mappingof the self-interference of a single quantum particle hitting an obstacle.
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Physical systems made of many interacting quantum particles can often be described by Euler hydrodynamic equations in the limit of long wavelengths and low frequencies. Recently such a classical hydrodynamic framework, now dubbed Generalized Hydrodynamics (GHD), was found for quantum integrable models in one spatial dimension. Despite its great predictive power, GHD, like any Euler hydrodynamic equation, misses important quantum effects, such as quantum fluctuations leading to non-zero equal-time correlations between fluid cells at different positions. Focusing on the one-dimensional gas of bosons with delta repulsion, and on states of zero entropy, for which quantum fluctuations are larger, we reconstruct such quantum effects by quantizing GHD. The resulting theory of quantum GHD can be viewed as a multi-component Luttinger liquid theory, with a small set of effective parameters that are fixed by the Thermodynamic Bethe Ansatz. It describes quantum fluctuations of truly nonequilibrium systems where conventional Luttinger liquid theory fails.
Exciton Mott physics in two-dimensional electron-hole (e-h) systems is studied in the quasiequilibrium, which is the crossovers or phase transitions between the insulating exciton gas and the metallic e-h plasma. By developing a self-consistent screened T-matrix approximation, we succeed in obtaining the global phase diagram on the plane of the e-h density and the temperature as a contour plot of the exciton ionization ratio. The detailed features of the exciton-Mott crossover at high temperature are figured out beyond the conventionally used concept of the Mott density. At low temperature, we find not only the region unstable toward the inhomogeneity but the pure Mott transition point characterized by the discontinuity in the ionization ratio. The single particle spectra also exhibit interesting features reflecting the excitonic correlations.
The Kibble-Zurek mechanism provides a unified theory to describe the universal scaling laws in the dynamics when a system is driven through a second-order quantum phase transition. However, for first-order quantum phase transitions, the Kibble-Zurek mechanism is usually not applicable. Here, we experimentally demonstrate and theoretically analyze a power-law scaling in the dynamics of a spin-1 condensate across a first-order quantum phase transition when a system is slowly driven from a polar phase to an antiferromagnetic phase. We show that this power-law scaling can be described by a generalized Kibble-Zurek mechanism. Furthermore, by experimentally measuring the spin population, we show the power-law scaling of the temporal onset of spin excitations with respect to the quench rate, which agrees well with our numerical simulation results. Our results open the door for further exploring the generalized Kibble-Zurek mechanism to understand the dynamics across first-order quantum phase transitions.
We present a new theoretical framework for describing an impurity in a trapped Bose system in one spatial dimension. The theory handles any external confinement, arbitrary mass ratios, and a weak interaction may be included between the Bose particles. To demonstrate our technique, we calculate the ground state energy and properties of a sample system with eight bosons and find an excellent agreement with numerically exact results. Our theory can thus provide definite predictions for experiments in cold atomic gases.
The Higgs amplitude mode is a collective excitation studied and observed in a broad class of matter, including superconductors, charge density waves, antiferromagnets, 3He p-wave superfluid, and ultracold atomic condensates. In all the observations reported thus far, the amplitude mode was excited by perturbing the condensate out of equilibrium. Studying an exciton-polariton condensate, here we report the first observation of this mode purely driven by intrinsic quantum fluctuations without such perturbations. By using an ultrahigh quality microcavity and a Raman spectrometer to maximally reject photoluminescence from the condensate, we observe weak but distinct photoluminescence at energies below the condensate emission. We identify this as the so-called ghost branches of the amplitude mode arising from quantum depletion of the condensate into this mode. These energies, as well as the overall structure of the photoluminescence spectra, are in good agreement with our theoretical analysis.
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