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Generation of optical signal and terahertz idler photons by spontaneous parametric down-conversion
摘要： Frequency-angular characteristics of signal and idler photons generated under spontaneous parametric down-conversion are studied in a strongly frequency nondegenerate regime, without paraxial approximation, accounting for possible inherent absorption of idler waves in a nonlinear crystal, classical thermal field fluctuations, and the multimode character of parametric interaction induced by transverse spatial limitation of the pump beam. Spatial limitation is shown to lead to a huge increase in angular divergence of the idler photons generated at terahertz frequencies. General expressions are obtained for the frequency-angular sensitivity function of the nonlinear-optical terahertz wave detector and for power densities of the signal and idler photon fluxes. The absorption-induced difference in the parametric conversion coefficients for the noise and externally incident radiation of the idler frequency is shown to be described by approximately the same loss factor for all active spatial idler modes. Two different parametric contributions of the internal thermal noise to the number of output idler photons were revealed with different dependence on the idler-wave absorption. Expressions for the loss factors, which describe absorption-induced effects in signal and idler channels, are obtained and shown to be turning into one another by changing the sign of the absorption coefficient. Relative contribution of thermal and quantum field fluctuations into the intrinsic radiation of a nonlinear crystal at signal and idler frequencies is analyzed accounting for the crystal absorption properties.
关键词： nonlinear optics,thermal fluctuations,terahertz,quantum fluctuations,absorption,spontaneous parametric down-conversion
更新于2025-09-23 15:22:29
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Atomic swap gate, driven by position fluctuations, in dispersive cavity optomechanics
摘要： Tracing the dynamics of a quantum system using a mesoscopic device is an important topic of interest nowadays. Here we show how a mesoscopic mechanical oscillator can be used to steer the dynamics of a coupled two-atom system and thereby to implement a two-qubit universal gate. We have theoretically studied a generic hybrid atom-optomechanical system where two identical atoms in Λ configuration are trapped inside the cavity and the cavity mode mediates the interaction between the atoms and the mechanical oscillator. Adiabatic elimination of the lossy channels, namely, cavity decay and spontaneous emission, is adopted to obtain an effective Hamiltonian. This Hamiltonian is responsible for two-atom swap and √SWAP gates, controlled by the position fluctuation of the oscillator. The validity of the proposal for successful implementation is assessed using presently available experimental parameters.
关键词： quantum gate,trapped atoms,quantum fluctuations,Cavity optomechanics
更新于2025-09-23 15:21:21
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revealed by high-energy x-ray diffraction
摘要： We explore the evolution of the structural phase transition of (Sr, Ca)3Ir4Sn13, a model system to study the interplay between structural quantum criticality and superconductivity, by means of high-energy x-ray diffraction measurements at high pressures and low temperatures. Our results confirm a rapid suppression of the superlattice transition temperature T ? against pressure, which extrapolates to zero at a critical pressure of ≈1.79(4) GPa. The temperature evolution of the superlattice Bragg peak in Ca3Ir4Sn13 reveals a drastic decrease of the intensity and an increase of the linewidth when T → 0 K and p → pc. Such anomaly is likely associated with the emergence of quantum fluctuations that disrupt the formation of long-range superlattice modulation. The revisited temperature-pressure phase diagram of (Sr, Ca)3Ir4Sn13 thus highlights the intertwined nature of the distinct order parameters present in this system and demonstrates some similarities between this family and the unconventional superconductors.
关键词： high-energy x-ray diffraction,structural phase transition,superconductivity,quantum criticality,quantum fluctuations
更新于2025-09-23 15:19:57
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Elusive torque sensed by liquid crystals
摘要： Almost half a century ago, it was predicted that the confinement of quantum fluctuations could induce mechanical rotation — the Casimir torque. This prediction has now been confirmed using liquid crystals. See Letter p.386
关键词： quantum fluctuations,liquid crystals,Casimir torque,mechanical rotation
更新于2025-09-04 15:30:14