arXiv subjects

Yingwen Zhang

Publications and source records attributed to Yingwen Zhang.

At least 37 records · Page 2Linked to original sources

arXiv2023

Topological superconductivity with large Chern numbers in a ferromagnetic metal-superconductor heterostructure

The ferromagnetic metal-superconductor heterostructure with interface Rashba spin-orbit hopping is a promising candidate for topological superconductivity. We study the interplay between the interface Rashba hopping and the intrinsic Dresselhaus spin-orbit coupling in this heterostructure, and demonstrate rich topological phases with five distinct Chern numbers. In particular, we find a topological state with a Chern number as large as four in the parameter space of the heterostructure. We calculate the Berry curvatures that construct the Chern numbers, and show that these Berry curvatures induce anomalous thermal Hall transport of the superconducting quasiparticles. We reveal chiral edge states in the topological phases, as well as helical edge states in the trivial phase, and show that the wave functions of these edge states mostly concentrate on the ferrometal layer of the heterostructure.

cond-mat.supr-con↗

arXiv2023

Full spatial characterization of entangled structured photons

Vector beams (VBs) are fully polarized beams with spatially varying polarization distributions, and they have found widespread use in numerous applications such as microscopy, metrology, optical trapping, nano-photonics, and communications. The entanglement of such beams has attracted significant interest, and it has been shown to have tremendous potential in expanding existing applications and enabling new ones. However, due to the complex spatially varying polarization structure of entangled VBs (EVBs), a complete entanglement characterization of these beams remains challenging and time-consuming. Here, we have used a time-tagging event camera to demonstrate the ability to simultaneously characterize approximately $2.6\times10^6$ modes between a bi-partite EVB using only 16 measurements. This achievement is an important milestone in high-dimensional entanglement characterization of structured light, and it could significantly impact the implementation of related quantum technologies. The potential applications of this technique are extensive, and it could pave the way for advancements in quantum communication, quantum imaging, and other areas where structured entangled photons play a crucial role.

quant-ph↗

arXiv2023

Quantum correlation light-field microscope with extreme depth of field

Light-field microscopy (LFM) is a 3D microscopy technique whereby volumetric information of a sample is gained by simultaneously capturing both the position and momentum (angular) information of light illuminating a scene. Conventional LFM designs generally require a trade-off between position and momentum resolution, requiring one to sacrifice resolving power for increased depth of field (DOF) or vice versa. In this work, we demonstrate a LFM design that does not require this trade-off by utilizing the inherent correlations between spatial-temporal entangled photon pairs. Here, one photon from the pair is used to illuminate a sample from which the position information of the photon is captured directly by a camera. By virtue of the strong momentum anti-correlation between the two photons, the momentum information of the illumination photon can then be inferred by measuring the angle of its entangled partner on a different camera. By using a combination of ray-tracing and a Gerchberg-Saxton type algorithm for the light field reconstruction, we demonstrate that a resolving power of 5 $μ$m can be maintained with a DOF of $\sim500$ $μ$m, approximately 3 times of the latest LFM designs or $>100$ time that of a conventional microscope. In the extreme, at a resolving power of 100 $μ$m, it is possible to achieve near infinite DOF.

quant-ph↗

arXiv2022

Experimental realisations of the fractional Schrödinger equation in the temporal domain

The fractional Schrödinger equation (FSE) -- a natural extension of the standard Schrödinger equation -- is the basis of fractional quantum mechanics. It can be obtained by replacing the kinetic-energy operator with a fractional derivative. Here, we report the experimental realisation of an optical FSE for femtosecond laser pulses in the temporal domain. Programmable holograms and the single-shot measurement technique are respectively used to emulate a \textit{Lévy waveguide} and to reconstruct the amplitude and phase of the pulses. Varying the Lévy index of the FSE and the initial pulse, the temporal dynamics is observed in diverse forms, including solitary, splitting and merging pulses, double Airy modes, and ``rain-like'' multi-pulse patterns. Furthermore, the transmission of input pulses carrying a fractional phase exhibits a ``fractional-phase protection'' effect through a regular (non-fractional) material. The experimentally generated fractional time-domain pulses offer the potential for designing optical signal-processing schemes.

physics.optics↗

arXiv2022

Reconfigurable phase contrast microscopy with correlated photon pairs

A phase-sensitive microscopy technique is proposed and demonstrated that employs the momentum correlations inherent in spontaneous parametric down-conversion. One photon from a correlated pair is focused onto a microscopic target while the other is measured in the Fourier plane. This provides knowledge of the position and angle of illumination for every photon striking the target, allowing full post-production control of the illumination angle used to form an image. The versatility of this approach is showcased with asymmetric illumination and differential phase contrast imaging, without any beam blocks or moving parts.

quant-ph↗

arXiv2022

Characterisation of a single photon event camera for quantum imaging

We show a simple yet effective method that can be used to characterize the per pixel quantum efficiency and temporal resolution of a single photon event camera for quantum imaging applications. Utilizing photon pairs generated through spontaneous parametric down-conversion, the detection efficiency of each pixel, and the temporal resolution of the system, are extracted through coincidence measurements. We use this method to evaluate the TPX3CAM, with appended image intensifier, and measure an average efficiency of 7.4% and a temporal resolution of 7.3ns. Furthermore, this technique reveals important error mechanisms that can occur in post-processing. We expect that this technique, and elements therein, will be useful to characterise other quantum imaging systems.

quant-ph↗

arXiv2022

Manipulating the symmetry of transverse momentum entangled biphoton states

Bell states are a fundamental resource in photonic quantum information processing. These states have been generated successfully in many photonic degrees of freedom. Their manipulation, however, in the momentum space remains challenging. Here, we present a scheme for engineering the symmetry of two-photon states entangled in the transverse momentum degree of freedom through the use of a spatially variable phase object. We demonstrate how a Hong-Ou-Mandel interferometer must be constructed to verify the symmetry in momentum entanglement via photon "bunching"/"anti-bunching" observation. We also show how this approach allows generating states that acquire an arbitrary phase under the exchange operation.

quant-ph↗

arXiv2022

High-speed imaging of spatiotemporal correlations in Hong-Ou-Mandel interference

The Hong-Ou-Mandel interference effect lies at the heart of many emerging quantum technologies whose performance can be significantly enhanced with increasing numbers of entangled modes one could measure and thus utilize. Photon pairs generated through the process of spontaneous parametric down conversion are known to be entangled in a vast number of modes in the various degrees of freedom (DOF) the photons possess such as time, energy, and momentum, etc. Due to limitations in detection technology and techniques, often only one such DOFs can be effectively measured at a time, resulting in much lost potential. Here, we experimentally demonstrate, with the aid of a time tagging camera, high speed measurement and characterization of two-photon interference. {With a data acquisition time of only a few seconds, we observe a bi-photon interference and coalescence visibility of $\sim64\%$ with potentially up to $\sim2\times10^3$ spatial modes}. These results open up a route for practical applications of using the high dimensionality of spatiotemporal DOF in two-photon interference, and in particular, for quantum sensing and communication.

quant-ph↗

arXiv2022

Snapshot hyperspectral imaging with quantum correlated photons

Hyperspectral imaging (HSI) has a wide range of applications from environmental monitoring to biotechnology. Current snapshot HSI techniques all require a trade-off between spatial and spectral resolution and are thus unable to achieve high resolutions in both simultaneously. Additionally, the techniques are resource inefficient with most of the photons lost through spectral filtering. Here, we demonstrate a snapshot HSI technique utilizing the strong spectro-temporal correlations inherent in entangled photons using a modified quantum ghost spectroscopy system, where the target is directly imaged with one photon and the spectral information gained through ghost spectroscopy from the partner photon. As only a few rows of pixels near the edge of the camera are used for the spectrometer, almost no spatial resolution is sacrificed for spectral. Also since no spectral filtering is required, all photons contribute to the HSI process making the technique much more resource efficient.

physics.optics↗

arXiv2022

Observation of Nonclassical Photon Statistics in Single-Bubble Sonoluminescence

A cavitation bubble inside a liquid, under a specific set of conditions, can get trapped in an antinode of the ultrasonically driven standing wave and periodically emits visible photons (1,2). This conversion of sound to light phenomenon, known as sonoluminescence, can be seen with unaided eyes and occurs in multi- or single-bubble regimes. The sonoluminescence radiation spectrum analysis attributes a temperature of about 6,000 Kelvin to the bubble (3-5) -- close to the sun's surface temperature. The bubble dynamics, thermodynamics, and other physicochemical properties are well-explored and studied over the past decades (6-8). Notwithstanding that several theories such as the thermal (black-body radiation) model (9-11), shock wave theory (12), phase transition radiation (13,14), and vacuum quantum electrodynamics (15,16) -- were proposed, the underlying physics of sonoluminescence has hitherto remained a puzzle. Here, we experimentally investigated the photon number statistics of the emitted photons from single-bubble sonoluminescence (SBSL), employing two distinctly different techniques, i.e., measuring multiphoton correlations and photon number (using a photon-number resolving detector). Our findings show that the emitted photons from SBSL possess sub-Poissonian statistics, indicating the nonclassical nature of the SBSL. Our observation of sub-Poissonian statistics of emitted photons may help to explain the physics of SBSL. In addition, considering the importance of nonclassical light sources in quantum technologies, this discovery would be an exciting milestone in paving the route towards a bright quantum photonics source.

quant-ph↗

arXiv2021

Ray-tracing with quantum correlated photons to image a 3D scene

To capture the 3D information of a scene, conventional techniques often require multiple 2D images of the scene to be captured from different perspectives. In this work we demonstrate the reconstruction of a scene's 3D information through ray-tracing using quantum correlated photon pairs. By capturing the two photons in different image planes using time-tagging cameras and taking advantage of the position, momentum and time correlation of the photons, the photons' propagation trajectory can be reconstructed. With this information on every photon pair, we were able to demonstrate refocusing, depth of field adjustment and parallax visualization of a 3D scene. With future camera advancements, this technique could achieve a much higher momentum resolution than conventional techniques thus giving larger depth of field and more viewing angles. The high photon correlation and low photon flux from a quantum source also makes the technique well suited for 3D imaging of light sensitive samples.

quant-ph↗

arXiv2021

High Speed Imaging of Spectral-Temporal Correlations in Hong-Ou-Mandel Interference

In this work we demonstrate spectral-temporal correlation measurements of the Hong-Ou-Mandel (HOM) interference effect with the use of a spectrometer based on a photon-counting camera. This setup allows us to take, within seconds, spectral temporal correlation measurements on entangled photon sources with sub-nanometer spectral resolution and nanosecond timing resolution. Through post processing, we can observe the HOM behaviour for any number of spectral filters of any shape and width at any wavelength over the observable spectral range. Our setup also offers great versatility in that it is capable of operating at a wide spectral range from the visible to the near infrared and does not require a pulsed pump laser for timing purposes. This work offers the ability to gain large amounts of spectral and temporal information from a HOM interferometer quickly and efficiently and will be a very useful tool for many quantum technology applications and fundamental quantum optics research.

physics.optics↗

arXiv2020

Quantum-Assisted Optical Interferometers: Instrument Requirements

It has been recently suggested that optical interferometers may not require a phase-stable optical link between the stations if instead sources of quantum-mechanically entangled pairs could be provided to them, enabling extra-long baselines and benefiting numerous topics in astrophysics and cosmology. We developed a new variation of this idea, proposing that photons from two different sources could be interfered at two decoupled stations, requiring only a slow classical connection between them. We show that this approach could allow high-precision measurements of the relative astrometry of the two sources, with a simple estimate giving angular resolution of $10 \ μ$as in a few hours' observation of two bright stars. We also give requirements on the instrument for these observations, in particular on its temporal and spectral resolution. Finally, we discuss possible technologies for the instrument implementation and first proof-of-principle experiments.

astro-ph.IM↗

arXiv2020

Experimental tests of Multiplicative Bell Inequalities

Bell inequalities are mathematical constructs that demarcate the boundary between quantum and classical physics. A new class of multiplicative Bell inequalities originating from a volume maximization game (based on products of correlators within bipartite systems) has been recently proposed. For these new Bell parameters, it is relatively easy to find the classical and quantum, i.e. Tsirelson, limits. Here, we experimentally test the Tsirelson bounds of these inequalities using polarisation-entangled photons for different number of measurements ($n$), each party can perform. For $n=2, 3, 4$, we report the experimental violation of local hidden variable theories. In addition, we experimentally compare the results with the parameters obtained from a fully deterministic strategy, and observe the conjectured nature of the ratio. Finally, utilizing the principle of "relativistic independence" encapsulating the locality of uncertainty relations, we theoretically derive and experimentally test new richer bounds for both the multiplicative and the additive Bell parameters for $n=2$. Our findings strengthen the correspondence between local and nonlocal correlations, and may pave the way for empirical tests of quantum mechanical bounds with inefficient detection systems.

quant-ph↗

arXiv2020

Automatic Gain Control Design for Dynamic Visible Light Communication Systems

For dynamic visible light communication (VLC) systems, received optical power fluctuates largely due to the fast movement of VLC terminals. Such fluctuations will cause possible signal clipping and quantization noise at the analog-to-digital converters (ADCs) and thus aggravate signal-to-noise ratio (SNR) and reliability of the communication link. To mitigate this effect, the automatic gain control (AGC) technique is often introduced in the receiver front-end to adaptively adjust the electrical signal strength. In this paper, we provided a VLC front-end analysis considering AGC model. Based on the model, some design principles of AGC are theoretically derivated: the effects of AGC index $m$, AGC maximum gain $g_{max}$ and AGC equilibrium range $DR$. Next, an analog AGC amplifier was carefully implemented and the effectiveness of our AGC modeling was proved through BER experiments. Finally, realtime 25Mb/s on-off-keying (OOK) experiments with AGC function were demonstrated in a dynamic link with different speeds. Experimental results show that the AGC can stabilize the BER performance and improve the system performance in the speed of 1m/s.

eess.SP↗

arXiv2020

Multivariate Discrimination in Quantum Target Detection

We describe a simple multivariate technique of likelihood ratios for improved discrimination of signal and background in multi-dimensional quantum target detection. The technique combines two independent variables, time difference and summed energy, of a photon pair from the spontaneous parametric down-conversion source into an optimal discriminant. The discriminant performance was studied in experimental data and in Monte-Carlo modelling with clear improvement shown compared to previous techniques. As novel detectors become available, we expect this type of multivariate analysis to become increasingly important in multi-dimensional quantum optics.

quant-ph↗

arXiv2020

Two-photon interference: the Hong-Ou-Mandel effect

Nearly 30 years ago, two-photon interference was observed, marking the beginning of a new quantum era. Indeed, two-photon interference has no classical analogue, giving it a distinct advantage for a range of applications. The peculiarities of quantum physics may now be used to our advantage to outperform classical computations, securely communicate information, simulate highly complex physical systems and increase the sensitivity of precise measurements. This separation from classical to quantum physics has motivated physicists to study two-particle interference for both fermionic and bosonic quantum objects. So far, two-particle interference has been observed with massive particles, among others, such as electrons and atoms, in addition to plasmons, demonstrating the extent of this effect to larger and more complex quantum systems. A wide array of novel applications to this quantum effect is to be expected in the future. This review will thus cover the progress and applications of two-photon (two-particle) interference over the last three decades.

quant-ph↗

arXiv2020

Increasing two-photon entangled dimensions by shaping input beam profiles

Photon pair entangled in high dimensional orbital angular momentum (OAM) degree of freedom (DOF) has been widely regarded as a possible source in improving the capacity of quantum information processing. The need for the generation of a high dimensional maximally entangled state in the OAM DOF is therefore much desired. In this work, we demonstrate a simple method to generate a broader and flatter OAM spectrum, i.e. a larger spiral bandwidth (SB), of entangled photon pairs generated through spontaneous parametric down-conversion by modifying the pump beam profile. By investigating both experimentally and theoretically, we have found that an exponential pump profile that is roughly the inverse of the mode profiles of the single-mode fibers used for OAM detection will provide a much larger SB when compared to a Gaussian shaped pump.

quant-ph↗