Holographic storage of multiple coherence gratings in a Bose-Einstein condensate

We demonstrate superradiant conversion between a two-mode collective atomic state and a single-mode light field in an elongated cloud of Bose-condensed atoms. Two off-resonant write beams induce superradiant Raman scattering, producing two independent coherence gratings with different wave vectors in the cloud. By applying phase-matched read beams after a controllable delay, the gratings can be selectively converted into the light field also in a superradiant way. Because of the large optical density and the small velocity width of the condensate, a high conversion efficiency of >70% and a long storage time of >120 micros were achieved.     

Superradiant transitions between high-lying levels of Sr in an external electric field

Superradiant transitions were observed between high lying levels in Sr. The transitions react very sensitively to an external electric field. Superradiant cascades or one transition in a superradiant branching can be suppressed. The square root of the high of a superradiant pulse decreases with the second power of the electric field strength. This behaviour can be explained by calculations.Dedicated to Prof. Dr. Herbert Welling on the occasion of his 60th birthday     

Phase transition to superradiance in a multicomponent system

Abtract The study deals with the ground-state energy transition of a multicomponent atomic system from its normal state to the superradiant state when interacting with a multimode quantized electromagnetic field. The threshold conditions are determined.Alexander-von-Humboldt awardee     

Superradiant rayleigh scattering and collective atomic recoil lasing in a ring cavity

Collective interaction of light with an atomic gas can give rise to superradiant instabilities. We experimentally study the sudden buildup of a reverse light field in a laser-driven high-finesse ring cavity filled with ultracold thermal or Bose-Einstein condensed atoms. While superradiant Rayleigh scattering from atomic clouds is normally observed only at very low temperatures (i.e., well below 1 microK), the presence of the ring cavity enhances cooperativity and allows for superradiance with thermal clouds as hot as several 10 microK. A characterization of the superradiance at various temperatures and cooperativity parameters allows us to link it to the collective atomic recoil laser.     

Superradiant dissipative tunneling in a double p–i–n semiconductor heterostructure with thermal injection of electrons

We propose a semiconductor device with two p–i–n junctions maintained at two different temperatures. When the current injected in the device due to this temperature difference exceeds a threshold value, a superradiant field is created in the first gate that induces an additional current in the second gate. The injection current is amplified by this reaction loop. In this way, the heat flow between the two junctions is partially transformed in superradiant power.     

Topological superradiant state in Fermi gases with cavity induced spin–orbit coupling

Coherently driven atomic gases inside optical cavities hold great promise for generating rich dynamics and exotic states of matter. It was shown recently that an exotic topological superradiant state exists in a two-component degenerate Fermi gas coupled to a cavity, where local order parameters coexist with global topological invariants. In this work, we characterize in detail various properties of this exotic state, focusing on the feedback interactions between the atoms and the cavity field. In particular, we demonstrate that cavity-induced interband coupling plays a crucial role in inducing the topological phase transition between the conventional and topological superradiant states. We analyze the interesting signatures in the cavity field left by the closing and reopening of the atomic bulk gap across the topological phase boundary and discuss the robustness of the topological superradiant state by investigating the steady-state phase diagram under various conditions. Furthermore, we consider the interaction effect and discuss the interplay between the pairing order in atomic ensembles and the superradiance of the cavity mode. Our work provides many valuable insights into the unique cavity–atom hybrid system under study and is helpful for future experimental exploration of the topological superradiant state.     

Opto-Mechanical Effects in Superradiant Light Scattering by Bose-Einstein Condensate in an Optical Cavity

We investigate the effects of a movable mirror (cantilever) of an optical cavity on the superradiant light scattering from a Bose-Einstein condensate (BEC) in an optical lattice. We show that the mirror motion has a dynamic dispersive effect on the cavity-pump detuning. Varying the intensity of the pump beam, one can switch between the pure superradiant regime and the Bragg scattering regime. The mechanical frequency of the mirror strongly influences the time interval between two Bragg peaks. We find that when the system is in the resolved side band regime for mirror cooling, the superradiant scattering is enhanced due to coherent energy transfer from the mechanical mirror mode to the cavity field mode.     

Opto-Mechanical Effects in Superradiant Light Scattering by Bose-Einstein Condensate in an Optical Cavity

We investigate the effects of a movable mirror (cantilever) of an optical cavity on the superradiant light scattering from a Bose-Einstein condensate (BEC) in an optical lattice. We show that the mirror motion has a dynamic dispersive effect on the cavity-pump detuning. Varying the intensity of the pump beam, one can switch between the pure superradiant regime and the Bragg scattering regime. The mechanical frequency of the mirror strongly influences the time interval between two Bragg peaks. We find that when the system is in the resolved side band regime for mirror cooling, the superradiant scattering is enhanced due to coherent energy transfer from the mechanical mirror mode to the cavity field mode.     

Spontaneous creation of massive spin half particles by a rotating block hole

The techniques of second quantization in Kerr metric for the scalar and neutrino (massless) fields are extended to the massive spin half case. The normal modes of Dirac field in Kerr metric are obtained in Chandrasekhar’s representation and the field is quantized as usual by imposing equal-time anti-commutation relations. The vacuum expectation value of energy-momentum tensor is evaluated asymptotically, leading to the result that a Kerr black hole spontaneously creates, in addition to scalar and neutrino quanta, massive Dirac particles in the classical superradiant modes.     

Superradiant free electron laser with space charge field

Linearized time dependent free electron laser equations with space charge field are solved for the space charge effects on the superradiant solution which now has a cosine square modulation on the intensity along the electron beam.     

Fluctuation in superradiance

The fluctuation of the intensity of superradiant pulse is calculated by applying a general asymptotic evaluation method of quantal macrovariables to a superradiant master equation. It is shown that the fluctuation of superradiant intensity is proportional to the cube of the number of the relevant atoms. The time-dependence of the proportional coefficient has been evaluated explicitly. It is predicted that there occurs an enhancement of fluctuation of superradiant intensity at an intermediate time. The intensity and fluctuation of higher order are also calculated. General expressions of expansion coefficients of a generating function are also given rigorously.     

Phase transition for coupled atom-light states in the presence of optical collisions

The problem of photon phase transition in a system of two-level atoms interacting with a quantized single-mode electromagnetic field in the presence of optical collisions is discussed. The photon field is shown to undergo a high-temperature second order phase transition into the coherent (superradiant) state at large negative values of atom-field detuning and under the condition of thermalization of coupled atom-light states.     

Superradiance triggering spectroscopy

The injection of a weak resonant field on a superradiant sample can induce large changes in the delay and spatial pattern of the emission. By measuring the change in direction of the emission lobes as a function of the injection field frequency, we have recorded the spectrum of the $\text{7P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{?}\text{7S}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ superradiant transition in cesium. As expected from theory, only a few photons per pulse are needed to record the spectrum. Various applications to very sensitive spectroscopy and to amplifier technology are discussed.     

Strong Coupling and Rabi Oscillations in GaAs/AlGaAs Heterostructures as a Result of Electron–Hole Pair Condensation at Room Temperature

JETP Letters - The experimental results of the investigation of coherent terahertz oscillations of the electromagnetic field from GaAs/AlGaAs heterostructures during the superradiant pulse...     

Quantum phase transition in the generalized single-mode superradiant model

In this paper we reveal a zero-temperature quantum phase transition for the single-mode superradiant model with the form A² from the normal to superradiant phase by mean of the Holstein-Primakoff transformation. In the thermodynamic limit, in which the numbers of atoms becomes infinite, the ground state energy and corresponding wavefunctions of both the normal and superradiant phases are obtained and therefore the scaling behavior near the critical transition point is derived.     

光泵NH3分子远红外激光研究

运用量子系统的密度矩阵理论，采用迭代法计算了光泵ＮＨ３分子远红外超辐射和腔式激光的频谱特性和相应的最佳工作气压。理论计算表明相对于超辐射方式，光泵腔式ＮＨ３分子远红外激光具有宽带辐射以及纵向调谐特性，且总的输出光强在一定条件下得到提高，最佳工作气压也较低。在实验上对ＴＥＡＣＯ２－１０Ｒ（８）和９Ｒ（１６）泵浦的Ｎ 红外超辐射和腔式激光器产生的远红外辐射进行了测量。结果表明理论计算与实验结果相符。     

Photon antibunching in the spontaneous emission from dicke's superradiant state

Quantum statistical properties of the spontaneous emission from a system of N identical two-level atoms in Dicke's superradiant state initially are studied analytically by solving exactly the superradiant master equation. It is found that photon antibunching exists in approximately the first half of the superradiant pulse duration.     

Field-driven super/subradiant lasing without inversion in three-level ladder scheme

A model of a superradiant laser comprising of N three-level systems driven by two pumping lasers is considered in semiclassical approximation. Steady-state equations for density matrix elements are solved both analytically and numerically. Various properties of generated light are investigated. It is found that such a laser can exhibit both superradiance, when the intensity scales as N(2), and subradiance when the intensity does not depend on N. The phase of the laser field is locked to the relative phase of the pumping lasers.     

Limited superradiant damping of small samples

We show that for samples small compared to a wavelength the maximum possible superradiant damping is severely limited by the shortness of the radiation-field-induced relaxation time T_Δ as compared to the superradiant lifetime T_S.