arXiv subjects

Shangqing Gong

Publications and source records attributed to Shangqing Gong.

At least 19 recordsLinked to original sources

arXiv2024

One-way multiple beam splitter designed by quantum-like shortcut-to-adiabatic passage

Based on the quantum mechanical "Shortcut-to-Adiabatic passage" (STAP), a novel design for the efficient and robust multiple beam splitter is presented in this paper. This multiple beam splitter consists of one input and $N$ output waveguide channels, which are connected via a mediator waveguide (WG). To implement "STAP" but without additional couplings, this $(N+2)$-WG system is first reduced to a controllable $3$-WGs counterpart by "Morris-Shore" (MS) transformation. Consequently, the reduced system can be directly compatible with all possible "STAP" methods. The results show that this novel design can achieve arbitrary ratio of multiple beam splitting and can significantly shorten the length of the device, which expands the application of "STAP" in classical system and provides a direct visualization in space of typical ultra-fast phenomena in time. More uniquely, this new design exhibits a one-way energy transport behavior. These may have profound impacts on exploring quantum technologies for promoting advanced optical devices.

physics.optics↗

arXiv2024

Highly Efficient Creation and Detection of Ultracold Deeply-Bound Molecules via Chainwise Stimulated Raman Shortcut-to-Adiabatic Passage

Chainwise stimulated Raman adiabatic passage (C-STIRAP) in M-type molecular system is a good alternative in creating ultracold deeply-bound molecules when the typical STIRAP in Λ-type system does not work due to weak Frank-Condon factors between states. However, its creation efficiency under the smooth evolution is generally low. During the process, the population in the intermediate states may decay out quickly and the strong laser pulses may induce multi-photon processes. In this paper, we find that shortcut-to-adiabatic (STA) passage fits very well in improving the performance of the C-STIRAP. Currently, related discussions on the so-called chainwise stimulated Raman shortcut-to-adiabatic passage (C-STIRSAP) are rare. Here, we investigate this topic under the adiabatic elimination. Given a relation among the four incident pulses, it is quite interesting that the M-type system can be generalized into an effective Λ-type structure with the simplest resonant coupling. Consequently, all possible methods of STA for three-state system can be borrowed. We take the counter-diabatic driving and "chosen path" method as instances to demonstrate our treatment on the molecular system. Although the "chosen path" method does not work well in real three-state system if there is strong decay in the excited state, our C-STIRSAP protocol under both the two methods can create ultracold deeply-bound molecules with high efficiency in the M-type system. The evolution time is shortened without strong laser pulses and the robustness of STA is well preserved. Finally, the detection of ultracold deeply-bound molecules is discussed.

quant-ph↗

arXiv2020

Kerr-type nonlinear optical isolators bypassing dynamic reciprocity

Magnetic-free optical isolators are critical components for the realization of integrated optical systems. The underlying physics of passive nonlinear optical isolators is not solely about breaking the Lorentz reciprocity without requiring any external bias. Indeed, one major obstacle to the operation of Kerr-type nonlinear optical isolators was found to be the so-called dynamic reciprocity, of which the serious outcome is that a backward signal cannot be isolated in the presence of a forward strong signal. In this work, we advocate the novel concept of velocity-selective nonlinearity to bypass such dynamic reciprocity. Using a proof-of-principle platform with warm rubidium atoms in an asymmetric cavity, we experimentally achieve the isolation of a backward signal in the presence of a strong forward signal, with experimental observations in agreement with our theoretical simulations. This work has thus made one essential step towards functioning Kerr-type passive optical isolators.

physics.optics↗

arXiv2014

Reversible self-Kerr-nonlinearity in an N-type atomic system through a switching field

We investigate the self-Kerr nonlinearity of a four-level N-type atomic system in 87Rb and observe its reversible property with the unidirectional increase of the switching field. For the laser arrangement that the probe field interacts with the middle two states, the slope and the sign of the self-Kerr nonlinearity around the atomic resonance can not only be changed from negative to positive, but also can be changed to negative again with the unidirectional increasing of the switching field. Numerical simulation agrees very well with the experimental results and dressed state analysis is presented to explain the experimental results.

physics.optics↗

arXiv2014

Phase-controlled Fano resonance by the nanoscale optomechanics

Observation of the Fano line shapes is essential to understand properties of the Fano resonance in different physical systems. We explore a tunable Fano resonance by tuning the phase shift in a Mach-Zehnder interferometer (MZI) based on a single-mode nano-optomechanical cavity. The Fano resonance is resulted from the optomechanically induced transparency caused by a nano-mechanical resonator and can be tuned by applying an optomechanical MZI. By tuning the phase shift in one arm of the MZI, we can observe the periodically varying line shapes of the Fano resonance, which represents an elaborate manipulation of the Fano resonance in the nanoscale optomechanics.

physics.optics↗

arXiv2014

Laser frequency offset locking via tripod-type electromagnetically induced transparency

We have demonstrated the laser frequency offset locking via the Rb tripod-type double dark resonances electromagnetically induced transparency (EIT) system. The influence of coupling fields power and detuning on the tripod-type EIT profile is detailed studied. In a wide coupling fields detuning range, the narrower EIT dip has an ultranarrow linewidth of 590 KHz, which is about one order narrower than the natural linewidth of Rb. Without the additional frequency stabilization of the coupling lasers, we achieve the relative frequency fluctuation of 60 KHz in a long time of ~2000s, which is narrower than the short-time linewidth of each individual laser.

physics.optics↗

arXiv2013

Observation of Multi-Electromagnetically Induced Transparency in V-type Rubidium atoms

A detailed experimental investigation and theoretical analysis have been made in the V-type 85Rb atomic medium. Seven induced transparency windows, including a central double-peak-structure, have been observed experimentally when a coupling field and a probe field are applied into the ground and first excited states. By taking into account the hyperfine splitting of the excited state, our theoretical analysis gives good explanation for the observed phenomena.

physics.optics↗

arXiv2013

Tunable frequency reference by optical pumping-assisted intracavity V-type electromagnetically induced transparency

A tunable high resolution frequency reference is constructed using the narrowed cavity-linewidth by the optical pumping-assisted V-type electromagnetically induced transparency (EIT). At room temperature, the optical pumping effect will increase the transparency for the V-type EIT and therefore the cavity-linewidth can be narrowed apparently. For the seven EITs observed in our previous study, cavity-linewidth narrowing is observed in all of them. More importantly, we find that the cavity-linewidth can keep at 1.2MHz in a wide frequency range of 100MHz by utilizing the central EIT. This property provides a novel way for constructing high resolution tunable frequency reference via the intracavity EIT.

physics.optics↗

arXiv2012

Tunneling-induced high efficiency four-wave mixing in an asymmetric quantum wells

An asymmetric double quantum wells (QWs) structure with resonant tunneling is suggested to achieve high efficient four wave mixing (FWM). We analytically demonstrate that the resonant tunneling can induce high efficient mixing wave in such a semiconductor structure with a low light pump wave. In particular, the FWM conversion efficiency can be enhanced dramatically in the vicinity of the center frequency. This interesting scheme may be used to generate coherent long-wavelength radiation in solid-state system.

quant-ph↗

arXiv2011

Realization of Single Attosecond Pulse Generation in Multi-Cycle Regime through Modulation of Carrier Wave

An intuitive physical mechanism for single attosecond pulse generation in multi-cycle pulse regime is proposed. We suggest that the continuum spectra of HHG can be controlled through the modulation of carrier wave, while keeping the multi-cycle envelope unchanged approximately. By increasing the time interval between the adjacent maximum return kinetic energy peaks, the kinetic energy of the side peaks will be apparently suppressed by the multi-cycle envelope. The photons with energies near the cutoff burst only at the pulse center with high coherence, which contribute to the generation of single attosecond pulse. We verify this mechanism by using a multi-cycle tri-color pulse as driver field.

physics.optics↗

arXiv2011

Strongly interacting and highly entangled photons in asymmetric quantum well with resonant tunneling

We propose an asymmetric quantum well structure to realize strong interaction between two slow optical pulses. The linear optical properties and nonlinear optical responses associated with cross-Kerr nonlinearity are analyzed. Combining the resonant tunneling and the advantages of inverted-Y type scheme, giant cross-Kerr nonlinearity can be achieved with vanishing absorptions. Based on the unique feature, we demonstrate that highly entangled photons can be produced and photonic controlled phase gate can be constructed. In this construction, the scheme is symmetric for the probe and signal pulses. Consequently, the condition of group velocity matching can be fulfilled by adjusting the initial electron distribution.

physics.optics↗

arXiv2010

Anomalous photoelectron spectrum caused by finite interaction time in few-cycle xuv laser pulses

With the development of laser technology, pulse length enters the optical cycle regime and hence the interaction time between laser pulse and atoms becomes prominent. We investigate this problem in this Letter through the photoelectron spectrum of hydrogen atom in few-cycle xuv laser pulses. By solving one-dimensional time-dependent Schrödinger equation, we find that due to the insufficient interaction time, the electron can not gain enough energy from optical field when escaping the bind of the nuclear and then the abnormality appears in the photoelectron spectrum: the peak of photoelectron spectrum shows red shift compared with the well-known Einstein photo-electric effect formula. The shift becomes large as the pulse duration decreases.

physics.optics↗

arXiv2010

Phase control of spatial interference from two duplicated two-level atoms

We report the phase control of spatial interference of resonance fluorescence from two duplicated two-level atoms, driving by two orthogonally polarized fields. In this closed-loop system, the relative phase is of crucial importance to the recovery of the interference patten in the fluorescence light even with strong driving.In order to improve the experimental realizability, we propose a scheme to recover the visibility with fixed relative phase by adjusting the relative intensities between the two driving fields or alternatively by using a standing-wave field.

quant-ph↗

arXiv2010

Voltage-controlled intracavity electromagnetically induced transparency with asymmetry quantum dots molecule

We theoretically investigate the phenomenon of voltage-controlled intracavity electromagnetically induced transparency with asymmetric double quantum dot system. The impact of voltage on frequency pulling and cavity linewidth narrowing are discussed. The linewidth and position of the cavity transmission can be engineered by the bias voltage. The scheme may be useful in integrated electro-optical device in quantum information process.

quant-ph↗

arXiv2009

Tunneling-induced coherent electron population transfer in an asymmetric quantum well

We propose an asymmetric double quantum well structure with a common continuum and investigate the effect of resonant tunneling on the control of coherent electron population transfer between the two quantum wells. By numerically solving the motion equations of element moments, the almost complete electron population transfer from initial subband to the target subband could be realized due to the constructive interference via flexibly adjusting the structure parameters.

quant-ph↗

arXiv2009

Optical rotation of heavy hole spins by non-Abelian geometrical means

A non-Abelian geometric method is proposed for rotating of heavy hole spins in a singly positive charged quantum dot in Voigt geometry. The key ingredient is the delay-dependent non-Abelian geometric phase, which is produced by the nonadiabatic transition between the two degenerate dark states. We demonstrate, by controlling the pump, the Stokes and the driving fields, that the rotations about $y$- and $z$-axes with arbitrary angles can be realized with high fidelity. Fast initialization and heavy hole spin state readout are also possible.

quant-ph↗

arXiv2009

Sub-50 attosecond pulse generation from multicycle nonlinear chirped pulses

We present a method of producing single attosecond pulses by high-order harmonic generation with multi-cycle nonlinear chirped driver laser pulses. The symmetry of the laser feld in several optical cycles near the pulse center is dramatically broken, and then the photons which cover a much broad spectrum burst almost only in one optical cycle. So an ultra-broad continuum spectrum appears in the high order harmonic spectrum, from which an isolated sub-50 attosecond pulse could be obtained. The results are almost independent of the length and chirp form of the driver laser pulse.

physics.optics↗

arXiv2008

Control the high-order harmonics cutoff through the combination of chirped laser and static electric field

The high harmonic generation from atoms in the combination of chirped laser pulse and static field is theoretically investigated. For the first time, we explore a further physical mechanism of the significant extension of high harmonic generation cutoff based on three-step model. It is shown that the cutoff is substantially extended due to the asymmetry of the combined field. If appropriate parameters are chosen, the cutoff of high harmonic generation can reach Ip+42Up. Furthermore, an ultrabroad super-continuum spectrum can be generated. When the phases are properly compensated for, an isolated 9 attosecond pulse can be obtained.

physics.optics↗