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Generation of single and periodically repeated powerful ultrashort microwave pulses
摘要： Generation of powerful ultrashort microwave pulses (USP) is of interest for a large number of practical applications, including radars with high resolution, plasma diagnostics, spectroscopy etc. In order to achieve this purpose many methods well-known in laser physics can be implemented in microwave electronics. In the last decade significant progress was achieved in generation of microwave USPs based on classical superradiance (SR) of extended electron bunches. Using of this effect a new type of pulse sources has been developed, which are capable of producing uniquely short (under 0.2–1 ns) electromagnetic pulses at super-high peak powers exceeding 1 GW in the millimeter waves (Ka-band) and 3 GW in the centimeter waves (X-band) with a repetition frequency up to several kilohertz [1]. A natural continuation of this research is related with the promotion of SR sources in shorter wavelengths ranges, where the oversized waveguides should be used. In the first part of this paper the results of the experimental observation of SR emission with excitation of a surface wave in the oversized periodically corrugated slow wave structures are presented. The experiments were based on a theoretical consideration in the frame of the quasi-optical approach. A periodic train of powerful ultrashort microwave pulses with a repetition frequency of 10–100 MHz can be generated in electron oscillators with a saturable absorber installed in the feedback loop [2]. The mechanism of pulse formation in this case is similar to the passive mode-locking [3] in laser physics where such pulses are also treated as dissipative solitons. The second part of this paper is devoted to the theoretical analysis of solitons generation in a mode-locked two-section microwave oscillator consisting of Cherenkov TWT and a Kompfner absorber in the feedback loop.
关键词： Cherenkov TWT,dissipative solitons,superradiance,ultrashort microwave pulses,Kompfner absorber,mode-locking
更新于2025-09-10 09:29:36
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Monte-Carlo simulations of superradiant lasing
摘要： We simulate the superradiant dynamics of ensembles of atoms in the presence of collective and individual atomic decay processes. We apply the Monte-Carlo wave-function method and identify quantum jumps in a reduced Dicke state basis, which reflects the permutation symmetry of the system. While the number of density matrix elements in the Dicke representation increases polynomially with atom number, the quantum jump dynamics populates only a single Dicke state at the time and thus efficient simulations can be carried out for tens of thousands of atoms. The superradiant pulses from initially excited atoms agree quantitatively with recent experimental results of strontium atoms but rapid atom loss in these experiments does not permit steady-state superradiance. By introducing an incident flux of new atoms to maintain a large average atom number, our theoretical calculations predict lasing with a millihertz linewidth despite rapid atom number fluctuations.
关键词： quantum jumps,lasing,superradiance
更新于2025-09-09 09:28:46
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Negative-temperature-state relaxation and reservoir-assisted quantum entanglement in double-spin-domain systems
摘要： Spin collective phenomena including superradiance are even today being intensively investigated with experimental tests performed based on state-of-the-art quantum technologies. Such attempts are not only for the simple experimental verification of predictions from the last century, but also as a motivation to explore new applications of spin collective phenomena and the coherent control of the coupling between spin ensembles and reservoirs. In this paper, we investigate the open quantum dynamics of two spin ensembles (double-spin domains) coupled to a common bosonic reservoir. We analyze in detail the dynamics of our collective state and its structure by focusing on both the symmetry and asymmetry of this coupled spin system. We find that when the spin size of one of the double domains is larger than that of the other domain, at the steady state this system exhibits two unusual collective behaviors: the negative-temperature-state relaxation in the smaller spin domain and the reservoir-assisted quantum entanglement between the two domains. These results are the consequence of the asymmetry of this system and the decoherence driven by the common reservoir.
关键词： negative-temperature-state relaxation,spin collective phenomena,bosonic reservoir,superradiance,quantum entanglement,quantum dynamics
更新于2025-09-09 09:28:46