Optimization performance of quantum endoreversible Otto machines with dual-squeezed reservoirs

We consider a quantum endoreversible Otto engine cycle and its inverse operation-Otto refrigeration cycle,employing two-level systems as the working substance and operating in dual-squeezed reservoirs.We demonstrate that the efficiency of heat engines at maximum work output and the coefficient of performance for refrigerators at the maximum c criterion will degenerate toη-=η_(C)/(2-η_(C))andε-=(√9+8ε_(C)-3)/2 when symmetric squeezing is satisfied,respectively.We also investigated the influences of squeezing degree on the performance optimization of quantum Otto heat engines at the maximum work output and refrigerators at the maximum X criterion.These analytical results show that the efficiency of heat engines at maximum work output and the coefficient of performance for refrigerators at the maximum X criterion can be improved,reduced or even inhibited in asymmetric squeezing.Furthermore,we also find that the efficiency of quantum Otto heat engines at maximum work output is lower than that obtained from the Otto heat engines based on a single harmonic oscillator system.However,the coefficient of performance of the corresponding refrigerator is higher.

Performance optimization on finite-time quantum Carnot engines and refrigerators based on spin-1/2 systems driven by a squeezed reservoir

We investigate the finite-time performance of a quantum endoreversible Carnot engine cycle and its inverse operation-Carnot refrigeration cycle,employing a spin-1/2 system as the working substance.The thermal machine is alternatively driven by a hot boson bath of inverse temperatureβ_(h)and a cold boson bath at inverse temperatureβ_(c)(>βh).While for the engine model the hot bath is constructed to be squeezed,in the refrigeration cycle the cold bath is established to be squeezed,with squeezing parameter r.We obtain the analytical expressions for both efficiency and power in heat engines and for coefficient of performance and cooling rate in refrigerators.We find that,in the high-temperature limit,the efficiency at maximum power is bounded by the analytical valueη_(+)=√sech(2r)(1-η_(C)),and the coefficient of performance at the maximum figure of merit is limited byε_(+)=√sech(2r)(1+ε_(C))/sech(2r)(1+ε_(C))-εC)-1,whereη_(C)=1-β_(h)/β_(c)andε_(C)=β_(h)/(β_(c)-β_(h))are the respective Carnot values of the engines and refrigerators.These analytical results are identical to those obtained from the Carnot engines based on harmonic systems,indicating that the efficiency at maximum power and coefficient at maximum figure of merit are independent of the working substance.

Phase-tailored assembly and encoding of dissipative soliton molecules

Self-assembly of particle-like dissipative solitons,in the presence of mutual interactions,emphasizes the vibrant concept of soliton molecules in varieties of laser resonators.Controllable manipulation of the molecular patterns,held by the degrees of freedom of internal motions,still remains challenging to explore more efficient and subtle tailoring approaches for the increasing demands.Here,we report a new phase-tailored quaternary encoding format based on the controllable internal assembly of dissipative soliton molecules.Artificial manipulation of the energy exchange of soliton-molecular elements stimulates the deterministic harnessing of the assemblies of internal dynamics.Self-assembled soliton molecules are tailored into four phase-defined regimes,thus constituting the phase-tailored quaternary encoding format.Such phase-tailored streams are endowed with great robustness and are resistant to significant timing jitter.All these results experimentally demonstrate the programmable phase tailoring and exemplify the application of the phase-tailored quaternary encoding,prospectively promoting high-capacity all-optical storage.

300 km ultralong fiber optic DAS system based on optimally designed bidirectional EDFA relays

Optical fiber distributed acoustic sensing(DAS)based on phase-sensitive optical time domain reflectometry(φ-OTDR)is in great demand in many long-distance application fields,such as railway and pipeline safety monitoring.However,the DAS measurement distance is limited by the transmission loss of optical fiber and ultralow backscattering power.In this paper,a DAS system based on multispan relay amplification is proposed,where the bidirectional erbium-doped fiber amplifier(EDFA)is designed as a relay module to amplify both the probe light and the backscattering light.In the theoretical noise model,the parameters of our system are carefully analyzed and optimized for a longer sensing distance,including the extinction ratio(ER),span number,span length,and gain of erbium-doped fiber amplifiers.The numerical simulation shows that a bidirectional EDFA relay DAS system can detect signals over 2500 km,as long as the span number is set to be more than 100.To verify the effectiveness of the scheme,a six-span coherent-detection-based DAS system with an optimal design was established,where the cascaded acoustic-optic modulators(AOMs)were used for a high ER of 104 dB.The results demonstrate that the signal at the far end of 300.2 km can be detected and recovered,achieving a high signal-to-noise ratio of 59.6 dB and a high strain resolution of 51.8■at 50 Hz with a 20 m spatial resolution.This is,to the best of our knowledge,a superior DAS sensing distance with such a high strain resolution.

Ultrafast temporal-spectral analysis probes isomeric dynamics in a dissipative soliton resonator

Self-assembly of dissipative solitons arouses versatile configurations of molecular complexes,enriching intriguing dynamics in mode-locked lasers.The ongoing studies fuel the analogy between matter physics and optical solitons,and stimulate frontier developments of ultrafast optics.However,the behaviors of multiple constituents within soliton molecules still remain challenging to be precisely unveiled,regarding both the intramolecular and intermolecular motions.Here,we introduce the concept of“soliton isomer”to elucidate the molecular dynamics of multisoliton complexes.The time-lens and time-stretch techniques assisted temporal-spectral analysis reveals the diversity of assembly patterns,reminiscent of the“isomeric molecule”.Particularly,we study the fine energy exchange during the intramolecular motions,therefore gaining insights into the degrees of freedom of isomeric dynamics beyond temporal molecular patterns.All these findings further answer the question of how far the matter-soliton analogy reaches and pave an efficient route for assisting the artificial manipulation of multisoliton structures.