Superradiance of ultracold cesium Rydberg |65D_(5/2)> → |66P_(3/2)>

We investigate Rydberg |65D_(5/2)> → |66P_(3/2)> superradiance in dense ultracold cesium atoms,where the ground atoms are excited to |65D_(5/2)> Rydberg states via two-photon excitation in a standard magneto-optical trap.The superradiant spectrum of |65D_(5/2)> → |66P_(3/2)> is obtained using the state-selective field ionization technique.We observe its dynamic evolution process by varying the delay time of ionization field td.The results show that the evolution process of |65D_(5/2)> →|66P_(3/2)> is much shorter than its radiation lifetime at room temperature,which verifies the superradiance effect.The dependence of the superradiance process on Rydberg atoms number N_(e) and principal quantum number n is investigated.The results show that the superradiance becomes faster with increasing N_(e),while it is suppressed for stronger van der Waals(vdW) interactions.Superradiance has potential applications in quantum technologies,and the Rydberg atom is an ideal medium for superradiance.Our system is effective for studying the strong two-body interaction between Rydberg atoms.

Ground-state phase diagram,symmetries,excitation spectra and finite-frequency scaling of the two-mode quantum Rabi model

We investigate the two-mode quantum Rabi model(QRM)describing the interaction between a two-level atom and a two-mode cavity field.The quantum phase transitions are found when the ratioηof transition frequency of atom to frequency of cavity field approaches infinity.We apply the Schrieffer–Wolff(SW)transformation to derive the low-energy effective Hamiltonian of the two-mode QRM,thus yielding the critical point and rich phase diagram of quantum phase transitions.The phase diagram consists of four regions:a normal phase,an electric superradiant phase,a magnetic superradiant phase and an electromagnetic superradiant phase.The quantum phase transition between the normal phase and the electric(magnetic)superradiant phase is of second order and associates with the breaking of the discrete Z_(2) symmetry.On the other hand,the phase transition between the electric superradiant phase and the magnetic superradiant phase is of first order and relates to the breaking of the continuous U(1)symmetry.Several important physical quantities,for example the excitation energy and average photon number in the four phases,are derived.We find that the excitation spectra exhibit the Nambu–Goldstone mode.We calculate analytically the higher-order correction and finite-frequency exponents of relevant quantities.To confirm the validity of the low-energy effective Hamiltonians analytically derived by us,the finite-frequency scaling relation of the averaged photon numbers is calculated by numerically diagonalizing the two-mode quantum Rabi Hamiltonian.

Matter Reactors

In a previous paper, we proposed that a QCD gas that may be a possible candidate for the general theory of gravity (GR) ether may be comprised of ud~du~ exotic mesons. A method to determine the effective mass of the ud~du~ exotic meson and the Friedmann-Robertson-Walker (FRW) metric scale factor equation of state dimensionless parameter, w, by measuring the pseudo-first order β decay rates expected to be inversely proportional to the QCD gas atmospheric density was given. Here, we propose to measure the β decay rate, t1/2, and the earth distance to the milky-way galaxy super massive black hole (SMBH), hSMBH, at the earth aphelion each year for several years, and fit the data with the linear curve: -lnt1/2 = ahSMBH + b. The slope parameter, a, and the free parameter, b, may be used to calculate the Kerr spin parameter and determine if the QCD gas density on the ergosphere remains constant in time, or alternatively, grows in time according to Corley and Jacobson’s proposed black hole laser process.

Emission Characteristics of the Side Radiation of Excited of the Layer of Alcohol Solution of Rhodamine 6G with the Round Geometric Shape

The spectral-spatial characteristics of the lateral radiation of a circular-shaped Rhodamine 6G solution layer were investigated. The layer is a part of the laser dye solution, which is in optical contact with the bottom of optical cylindrical cell, the shape of which determines the geometric shape of the exciting layer. Homogeneous excitation of this layer by the second harmonic of the Nd+: YAG (λ = 532 nm) laser is realized. Circular, plane-directed radiation, with a small, vertical, divergence was obtained from the edges of the excited layer. Is investigated experimentally the spectral and spatial characteristics of radiation. Excitation of the layer was performed from the side of the cuvette bottom. It turned out that within the concentrations of the dye in the solution from 0.12 to 0.03 wt%, the following processes are observed: 1) Plane-directed radiation, with a small vertical divergence, uniform in intensity, around the optical cell in the plane of the luminescent layer;2) An increase in the amplitude of radiation pulses with a decrease in the concentration of the dye in the solution;3) Shifting of the maximum of the emission spectrum to the short-wave region, significant narrowing of the radiation spectrum and decrease of the vertical divergence of radiation.

Dynamical Casimir effect in superradiant light scattering by Bose Einstein condensate in an optomechanical cavity

We investigate the effects of dynamical Casimir effect in superradiant light scattering by Bose-Einstein condensate in an optomechanical cavity. The system is studied using both classical and quantized mirror motions. The cavity frequency is harmonically modulated in time for both the cases. The main quantity of interest is the number of intracavity scattered photons. The system has been investigated under the weak and strong modulations. It has been observed that the amplitude of the scattered photons is more for the classical mirror motion than the quantized mirror motion. Also, initially, the amplitude of scattered photons is high for lower modulation amplitude than higher modulation amplitude. We also found that the behavior of the plots are similar under strong and weak modulations for the quantized mirror motion.

Ultra-thin Glass Film Coated with Graphene: A New Material for Spontaneous Emission Enhancement of Quantum Emitter

We propose an ultra-thin glass film coated with graphene as a new kind of surrounding material which can greatly enhance spontaneous emission rate(SER) of dipole emitter embedded in it. With properly designed parameters,numerical results show that SER-enhanced factors as high as 1.286 9 106 can be achieved. The influences of glass film thickness and chemical potential/doping level of graphene on spontaneous emission enhancement are also studied in this paper. A comparison is made between graphene and other coating materials such as gold and silver to see their performances in SER enhancement.

Theoretical study of superradiant masing with solid-state spins at room temperature

Steady-state superradiance and superradiant lasing attract significant attentions in the field of optical lattice clocks,but have not been achieved yet due to the technical challenges and atom loss problem.In this article,we propose that their counter-part may be observed in the microwave domain with solid-state spins,i.e.,nitrogen-vacancy center spins and pentacene molecular spins,coupled to microwave resonator at room temperature with realistic technical restrictions.To validate our proposal,we investigate systematically the system dynamics and steady-state by solving quantum master equations for the multi-level and multi-process dynamics of trillions of spins.Our calculations show that the superradiant Rabi oscillations occur firstly due to transitions among different Dicke states,and the subsequent continuous-wave superradiant masing can achieve a linewidth well below millihertz.Our work may guide further exploration of transient and steady-state superradiant masing with the mentioned and other solid-state spins systems.The ultra-narrow linewidth may find applications in deep-space communications,radio astronomy and high-precision metrology.

Boson star superradiance

Recently,it has been realized that in some systems internal space rotation can induce energy amplification for scattered waves,similar to rotation in real space.In particularly,it has been shown that energy extraction is possible for a Q-ball,a stationary non-topological soliton that is coherently rotating in its field space.In this paper,we generalize the analysis to the case of boson stars,and show that the same energy extraction mechanism still works for boson stars.

Superradiance of massive scalar particles around rotating regular black holes

Regular black holes,as part of an important attempt to eliminate the singularities in general relativity,have been of wide concern.Because the superradiance associated with rotating regular black holes plays an indispensable role in black hole physics,we calculate the superradiance related effects,i.e.,the superradiance instability and the energy extraction efficiency,for a scalar particle with a small mass around a rotating regular black hole,where the rotating regular black hole is constructed by the modified Newman-Janis algorithm.We analytically give the eigenfrequency associated with instability and the amplification factor associated with energy extraction.For two specific models,i.e.,the rotating Hayward and Bardeen black holes,we investigate how their regularization parameters affect the growth of instability and the efficiency of energy extraction from the two rotating regular black holes.We find that the regularization parameters give rise to different modes of the superradiance instability and the energy extraction when the rotation parameters vary.There are two modes for the growth of superradiance instability and four modes for the energy extraction.Our results show the diversity of superradiance in the competition between the regularization parameter and the rotation parameter for rotating regular black holes.

Hawking radiation received at infinity in higher dimensional Reissner-Nordstrom black hole spacetimes

In this study,we investigate the Hawking radiation in higher dimensional Reissner-Nordstrom black holes as received by an observer located at infinity.The frequency-dependent transmission rates,which deform the thermal radiation emitted in the vicinity of the black hole horizon,are evaluated numerically.In addition to those in four-dimensional spacetime,the calculations are extended to higher dimensional Reissner-Nordstrom metrics,and the results are observed to be sensitive to the spacetime dimension to an extent.Generally,we observe that the transmission coefficient practically vanishes when the frequency of the emitted particle approaches zero.It increases with frequency and eventually saturates to a certain value.For four-dimensional spacetime,the above result is demonstrated to be mostly independent of the metric's parameter and the orbital quantum number of the particle,when the location of the event horizon,rh,and the product of the charges of the black hole and the particle qQ are known.However,for higher-dimensional scenarios,the convergence becomes more gradual.Moreover,the difference between states with different orbital quantum numbers is observed to be more significant.As the magnitude of the product of charges qQ becomes more significant,the transmission coefficient exceeds 1.In other words,the resultant spectral flux is amplified,which results in an accelerated process of black hole evaporation.The relationship of the calculated outgoing transmission coefficient with existing results on the greybody factor is discussed.

Time-resolved study of the lasing emission from high vibrational levels of N2^+ pumped with circularly polarized femtosecond pulses

We experimentally investigated the forward 353.8 nm radiation from plasma filaments in pure nitrogen gas pumped by intense circularly polarized 800 nm femtosecond laser pulses.This emission line corresponds to the B^2Σu^+(u'=4)-X^2Σg^+(u=3)transition of nitrogen ions.In the presence of an external seeding pulse,the 353.8 nm signal was amplified by 3 orders of magnitude.Thanks to the much enhanced intensity,we performed time-resolved measurement of the amplified 353.8 nm emission based on the sum-frequency generation technique.It was revealed that the built-up time and duration of these emissions are both inversely proportional to the gas pressure,while the radiation peak power grows up nearly quadratically with pressure,indicating that the 353.8 nm radiation is of the nature of superradiance.

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 dynam- ics 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.

Emergent symmetry at superradiance transition of a Bose condensate in two crossed beam cavities

Recently an experiment on superradiant transition of a Bose condensate in two crossed beam cavities has been reported by Leonard et al. in Nature 543, 87 （2017）. The surprise is they find that across the superradiant transition, the cavity light can be emitted in any superposition of these two cavity modes. This indicates an additional U（1） symmetry that does not exist in the full Hamiltonian. In this paper we show that this symmetry is an emergent symmetry in the vicinity of the phase transition. We identify all the necessary conditions that are required for this emergent U（I ） symmetry and show that this experiment is a special case that satisfies these conditions. We further show that the superradiant transition in this system can also be driven to a first order one when the system is tuned away from the point having the emergent svmmetrv.

Superfluid-superradiant mixed phase of the interacting degenerate Fermi gas in an optical cavity

We investigate the ground-state properties of an attractively interacting degenerate Fermi gas coupling with a high-finesse optical cavity. We predict a new mixed phase with both the superfluid and superradiant properties for the intermediate fermion-fermion interaction and fermion-photon coupling strengths. Moreover, in this mixed phase a relatively large ratio of the scaled polarization to the dimensionless mean-field gap, which is in contrast to that in the conventional superfluid regime can be obtained. We also figure out rich phase diagrams depending crucially on the atomic resonant frequency(effective Zeeman field) and address briefly the experimental detection of our predicted quantum phases.

Pulse generation with ultra-superluminal pulse propagation in semiconductor heterostructures by superradiant-phase transition enhanced by transient coherent population gratings

This paper reports the observation of ultra-superluminal pulse propagation in multiple-contact semiconductor heterostructures in a superradiant emission regime,and shows definitively that it is a different class of emission from conventional spontaneous or stimulated emission.Coherent population gratings induced in the semiconductor medium under strong electrical pumping have been shown to cause a major decrease of the group refractive index,in the range of 5–40%.This decrease is much greater than that caused by conventional carrier depletion or chirp mechanisms.The decrease in refractive index in turn causes faster-than-c propagation of femtosecond pulses.The measurement also proves the existence of coherent amplification of electromagnetic pulses in semiconductors at room temperature,the coherence being strongly enhanced by interactions of the light with coherent transient gratings locked to carrier gratings.This pulse-generation technique is anticipated to have great potential in applications where highly coherent femtosecond optical pulses must be generated on demand.

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.

Superradiant Instability of D-Dimensional Reissner–Nordstr?m Black Hole Mirror System

We analytically study the superradiant instability of charged massless scalar field in the background of D-dimensional Reissner-Nordstr6m （RN） black hole caused by mirror-like boundary condition. By using the asymptotic matching method to solve the Klein-Gordon equation that governs the dynamics of scalar field, we have derived the expressions of complex parts of boxed quasinormal frequencies, and shown they are positive in the regime of superradiance. This indicates the charged scalar field is unstable in D-dimensional Reissner-Nordstr6m （RN） black hole surrounded by mirror. However, the numerical work to calculate the boxed quasinormal frequencies in this system is still required in the future.

Quantum dynamics of electric-dipole coupled defect centers in solids

We investigate the quantum dynamics of two defect centers in solids,which are coupled by vacuum-induced dipole-dipole interactions.When the interaction between defects and phonons is taken into account,the two coupled electron-phonon systems make up two equivalent multilevel atoms.By making Born-Markov and rotating wave approximations,we derive a master equation describing the dynamics of the coupled multilevel atoms.The results indicate the concepts of subradiant and superradiant states can be applied to these systems and the population transfer process presents different behaviors from those of the two dipolar-coupled two-level atoms due to the participation of phonons.

A superradiant maser with nitrogen-vacancy center spins

Recent experiments have demonstrated Rabi-oscillations, superradiant pulses and stimulated emission from negatively-charged nitrogen-vacancy(NV;) center spins in microwave resonators. These phenomena witness the kind of collective and strong coupling which has been the prerequisite for observation of superradiant lasing in the optical frequency regime. In this article, we investigate the possibility to employ coherence, present in both the collective NV-spin ensemble and the microwave field, to achieve a superradiant maser. Our calculations show that a superradiant maser with a linewidth below millihertz can be achieved with moderate kilohertz incoherent pumping of over 10;spins at room temperature. We show that the superradiant masing prevails in the presence of inhomogeneous broadening, and we present numerical and analytical studies of the dependence of the phenomenon on the various physical parameters.

Three dimensional study of harmonic operation at the Shanghai deep ultraviolet free electron laser

With the right choice of parameters in the free electron laser （FEL） scheme, the undulator can be primarily operated at high order harmonic modes and the harmonic radiation is expected to be significantly enhanced. Recently, the possibility of proof-of-principle harmonic operation experiments on the basis of the Shanghai deep ultraviolet （SDUV） FEL test facility has been studied. In this paper, the principle of harmonic operation, three dimensional numerical approaches, and detailed performances of proposed harmonic operation at SDUV FEL are presented.