arXiv subjects

Shengwang Du

Publications and source records attributed to Shengwang Du.

At least 37 records · Page 2Linked to original sources

arXiv2021

Wavelength conversion for single-photon polarization qubits through continuous variable quantum teleportation

A quantum internet connects remote quantum processors that need interact and exchange quantum signals over a long distance through photonic channels. However, these quantum nodes are usually composed of quantum systems with emitted photons unsuitable for long-distance transmission. Therefore, quantum wavelength conversion to telecom is crucial for long-distance quantum networks based on optical fiber. Here we propose wavelength conversion devices for single-photon polarization qubits using continuous variable quantum teleportation, which can efficiently convert qubits between near-infrared (780/795 nm suitable for interacting with atomic quantum nodes) and telecom wavelength (1300-1500 nm suitable for long-distance transmission). The teleportation uses entangled photon sources (i.e., non-degenerate two-mode squeezed state) that can be generated by four-wave mixing in rubidium atomic vapor cells, with a diamond configuration of atomic transitions. The entangled fields can be emitted in two orthogonal polarizations with locked relative phase, making them especially suitable for interfacing with single-photon polarization qubits. Our work paves the way for the realization of long-distance quantum networks.

quant-ph↗

arXiv2021

Hybrid entanglement between optical discrete polarizations and continuous quadrature variables

By coherently combining advantages while largely avoiding limitations of two mainstream platforms, optical hybrid entanglement involving both discrete and continuous variables has recently garnered widespread attention and emerged as a promising idea for building heterogenous quantum networks. Different from previous results, here we propose a new scheme to remotely generate hybrid entanglement between discrete-polarization and continuous-quadrature optical qubits heralded by two-photon Bell state measurement. As a novel nonclassical light resource, we further utilize it to discuss two examples of ways -- entanglement swapping and quantum teloportation -- in which quantum information processing and communications could make use of this hybrid technique.

quant-ph↗

arXiv2021

Scalability of all-optical neural networks based on spatial light modulators

Optical implementation of artificial neural networks has been attracting great attention due to its potential in parallel computation at speed of light. Although all-optical deep neural networks (AODNNs) with a few neurons have been experimentally demonstrated with acceptable errors recently, the feasibility of large scale AODNNs remains unknown because error might accumulate inevitably with increasing number of neurons and connections. Here, we demonstrate a scalable AODNN with programmable linear operations and tunable nonlinear activation functions. We verify its scalability by measuring and analyzing errors propagating from a single neuron to the entire network. The feasibility of AODNNs is further confirmed by recognizing handwritten digits and fashions respectively.

physics.optics↗

arXiv2020

Efficient production of a narrow-line erbium magneto-optical trap with two-stage slowing

We describe an experimental setup for producing a large cold erbium (Er) sample in a narrow-line magneto-optical trap (MOT) in a simple and efficient way. We implement a pair of angled slowing beams with respect to the Zeeman slower axis, and further slow down atoms exiting from the Zeeman slower. The second-stage slowing beams enable the narrow-line MOT to trap atoms exiting from the Zeeman slower with higher velocity. This scheme is particularly useful when the Zeeman slower is at low optical power without the conventional transverse cooling between an oven and a Zeeman slower, in which case we significantly improve the loading efficiency into the MOT and are able to trap more than $10^8$ atoms in the narrow-line MOT of $^{166}$Er. This work highlights our implementation, which greatly simplifies laser cooling and trapping of Er atoms and also should benefit other similar elements.

cond-mat.quant-gas↗

arXiv2019

Einstein-Podolsky-Rosen Energy-Time Entanglement of Narrowband Biphotons

We report the direct characterization of energy-time entanglement of narrowband biphotons produced from spontaneous four-wave mixing in cold atoms. The Stokes and anti-Stokes two-photon temporal correlation is measured by single-photon counters with nano second temporal resolution, and their joint spectrum is determined by using a narrow linewidth optical cavity. The energy-time entanglement is verified by the joint frequency-time uncertainty product of 0.063 +/- 0.0044, which does not only violate the separability criterion but also satisfies the continuous variable Einstein-Podolsky-Rosen steering inequality.

quant-ph↗

arXiv2019

Anti-Parity-Time Symmetric Optical Four-Wave Mixing in Cold Atoms

Non-Hermitian optical systems with parity-time (PT) symmetry have recently revealed many intriguing prospects that outperform conservative structures. The prevous works are mostly rooted in complex arrangements with controlled gain-loss interplay. Here, we demonstrate anti-PT symmetry inherent in nonlinear optical interactions based upon forward optical four-wave mixing in a laser-cooled atomic ensemble with negligible linear gain and loss. We observe the pair of frequency modes undergo a nontrivial anti-PT phase transition between coherent power oscillation and optical parametric amplification in presence of a large phase mismatch.

physics.optics↗

arXiv2019

All Optical Neural Network with Nonlinear Activation Functions

Artificial neural networks (ANNs) have now been widely used for industry applications and also played more important roles in fundamental researches. Although most ANN hardware systems are electronically based, optical implementation is particularly attractive because of its intrinsic parallelism and low energy consumption. Here, we propose and demonstrate fully-functioned all optical neural networks (AONNs), in which linear operations are programmed by spatial light modulators and Fourier lenses, and optical nonlinear activation functions are realized with electromagnetically induced transparency in laser-cooled atoms. Moreover, all the errors from different optical neurons here are independent, thus the AONN could scale up to a larger system size with final error still maintaining in a similar level of a single neuron. We confirm its capability and feasibility in machine learning by successfully classifying the order and disorder phases of a typical statistic Ising model. The demonstrated AONN scheme can be used to construct various ANNs of different architectures with the intrinsic parallel computation at the speed of light.

physics.optics↗

arXiv2018

Light Sheets with Extended Length

High resolution light-sheet optical microscopy requires illuminating a sample by a thin excitation light sheet with large area. Here, we describe methods for producing light sheets with extended length, as compared to Gaussian-beam-type diffracting light sheets with the same thickness, without scanning or dithering the light beams.

physics.optics↗

arXiv2018

Precise characterization of polarizing prisms by optical localization analysis

We utilize the localization analysis method to precisely determine the light beam positions with the spatial separation beyond the optical diffraction limit. By such a direct spatial measurement, the associated optical setup is built to characterize the beam-shear angle of polarizing prisms that refract the light propagation according to polarization. We use the Nomarski prisms to demonstrate our method. The statistical error is below 0.5 urad, which is two orders of magnitudes smaller than the tolerance value given by most prism manufacturers. Our method provides a stand-alone characterization of prisms with a high accuracy for many quantitative imaging technologies such as the orientation-free DIC microscope and the dual-focus fluorescence correlation spectroscopy.

physics.ins-det↗

arXiv2017

An integrated single- and two-photon non-diffracting light-sheet microscope

We describe the apparatus of a fluorescence optical microscope with both single-photon and two-photon non-diffracting light sheets excitation for large volume imaging. With special design to accommodate two different wavelength ranges (visible: 400-700 nm, and near infrared: 800-1200 nm), we combine the line-Bessel sheet (LBS, for single-photon excitation) and the scanning Bessel beam (SBB, for two-photon excitation) light sheet together in a single microscope setup. For a transparent thin sample where the scattering can be ignored, the LBS single-photon excitation is the optimal imaging solution. When the light scattering becomes significant for a deep-cell or deep-tissue imaging, we use SBB light-sheet two-photon excitation with a longer wavelength. We achieved nearly identical lateral/axial resolution of about 350/270 nm for both imagings. This integrated light-sheet microscope may have a wide application for live-cell and live-tissue three-dimensional high-speed imaging.

physics.ins-det↗

arXiv2016

Bell inequality of frequency-bin entangled photon pairs with time-resolved detection

Entanglement, describing the inseparability of a quantum multiparty system, is one of the most intriguing features of quantum mechanics. Violation of Bell inequality, for ruling out the possibility of local hidden variable theories, is commonly used as a strong witness for quantum entanglement. In previous Bell test experiments with photonic entanglement based on two-photon coincidence measurement, the photon temporal wave packets are absorbed completely by the detectors. That is, the photon coherence time is much shorter than the detection time window. Here we demonstrate generation of frequency-bin entangled narrowband biphotons, and for the first time, test the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality |S|<= 2 for their nonlocal temporal correlations with time-resolved detection. We obtain a maximum |S| value of 2.52+/-0.48 that violates the CHSH inequality. Our result will have applications in quantum information processing involving time-frequency entanglement.

quant-ph↗

arXiv2016

Subnatural-linewidth biphotons from a Doppler-broadened hot atomic vapor cell

We report the efficient generation of subnatural-linewidth (< 6 MHz, for Rb D1/D2 lines) biphotons from a Doppler-broadened (530 MHz) hot atomic vapor cell. We use on-resonance spontaneous four-wave mixing in a hot paraffin-coated 87Rb vapor cell at 63 C to produce time-frequency entangled photon pairs with controllable bandwidth (1.9 - 3.2 MHz) and coherence time (47 - 94 ns). Our backward phase-matching scheme with optical pumping is the key to minimize the generation of uncorrelated photons from resonance fluorescence. The result paves the way toward miniature narrowband biphoton source based on atomic cells

quant-ph↗

arXiv2015

Quantum-State Purity of Heralded Single Photons Produced from Frequency-Anti-Correlated Biphotons

We analyze the quantum-state purity of heralded single photons produced from frequency-anti-correlated biphotons. We find that the quantum-state purity in time-frequency domain depends strongly on the response time uncertainty of the trigger-photon detector that heralds the generation of its paired photon. If the trigger response time is much shorter than the two-photon coherence time, the time-frequency quantum-state purity of heralded single photons approaches unity and the heralded single photon is in a nearly pure state. If the trigger response time is much longer than the two-photon coherence time, the heralded photon is then projected onto a mixed state. Making use of the time-frequency entanglement, heralded single photons with a well-defined temporal wave function or a frequency superposition state can be produced and engineered. This time-frequency entanglement allows for shaping heralded single photons through nonlocal spectral modulation.

quant-ph↗

arXiv2015

Narrowband biphoton generation in the group delay regime

We study narrow-band biphoton generation from spontaneous four-wave mixing with electromagnetically induced transparency in a laser cooled atomic ensemble. We compare two formalisms in the interaction and Heisenberg pictures, and find that they agree in the low gain regime but disagree in the high gain regime. We extend both formalisms accounting the non-uniformity in atomic density and the driving laser fields. We find that for a fixed optical depth and a weak and far-detuned pump laser beam, the two-photon waveform is independent of the atomic density distribution. However, the spatial profiles of the two driving laser beams have significant effects on the biphoton temporal waveform. We predict that waveform shaping in time domain can be achieved by controlling the spatial profiles of the driving laser fields.

quant-ph↗

arXiv2015

Subwavelength Transportation of Light with Atomic Resonances

We propose and investigate a new type of optical waveguide made by an array of atoms without involving conventional Bragg scattering or total internal reflection. A finite chain of atoms collectively coupled through their intrinsic resonance supports a propagating mode with minimal radiative loss when the array spacing $a$ is around 0.6$λ_0/2π$ where $λ_0$ is the wavelength of the nearly resonant optical transition. We find that the transportation is robust with respect to position fluctuation and remains possible when the atoms are placed on a circle. Our result paves the way to implement the subwavelength transportation of light in integrated optical circuits with cold atoms.

cond-mat.mes-hall↗

arXiv2015

Frequency-Bin Entanglement with Tunable Phase

We describe a technique to produce narrow-band photon pairs with frequency-bin entanglement, whose relative phase can be tuned using linear polarization optics. We show that, making use of the polarization-frequency coupling effect, the phase of a complex polarizer can be transferred into the frequency entanglement.

quant-ph↗

arXiv2015

Narrowband Biphotons: Generation, Manipulation, and Applications

In this chapter, we review recent advances in generating narrowband biphotons with long coherence time using spontaneous parametric interaction in monolithic cavity with cluster effect as well as in cold atoms with electromagnetically induced transparency. Engineering and manipulating the temporal waveforms of these long biphotons provide efficient means for controlling light-matter quantum interaction at the single-photon level. We also review recent experiments using temporally long biphotons and single photons.

quant-ph↗

arXiv2014

Narrowband Biphotons with Polarization-Frequency Coupled Hyperentanglement

We demonstrate the generation of narrowband biphotons with polarization-frequency coupled hy- perentanglement from spontaneous four-wave mixing in cold atoms. The coupling between polariza- tion and frequency is realized through a frequency shifter and linear optics. When the polarization- frequency degrees of freedom are decoupled, it is robust to create polarization and frequency Bell states, confirmed by the polarization quantum-state tomography and the two-photon temporal quan- tum beating. Making use of the polarization-frequency coupling to transfer polarization phase retard to the entangled frequency modes, we produce a frequency Bell state with tunable phase difference between its two bases.

quant-ph↗