arXiv subjects

Chee Wei Wong

Publications and source records attributed to Chee Wei Wong.

At least 19 recordsLinked to original sources

arXiv2026

Magneto-optic phonon resonances in magnetic topological EuCd2As2 via helical Raman spectroscopy

EuCd2As2 materials have two magnetic ordering states: antiferromagnetic (AFM) and ferromagnetic (FM) when their chemical tunability is utilized. While AFM-EuCd2As2 has a nonzero magnetoelectric response due to its symmetry breaking with spin configuration, FM-EuCd2As2 is an ideal candidate for studies of Weyl physics because of its minimum number of Weyl points with opposite chirality. In this article, we examine cryogenic low-frequency Raman spectroscopy of phonon modes in FM-EuCd2As2 crystals using circular polarization configurations, with support from density functional theory calculations, and investigate in-plane magneto-anisotropy by linear polarization configuration below the Curie temperature (Tc = 26 K). We attribute the anomalous enhancements in Raman intensities below the Curie temperature are due to spin-phonon coupling. Furthermore, we see that A-mode peaks can be distinguished by magneto-helical Raman spectroscopy through the magneto-optic effect and that the degree of circular polarization (DCP) of 12.5 meV peak reaches 60% at 4.2 K and becomes saturated. We also examine AFM-EuCd2As2 below Néel temperature (TN = 9 K) to compare with FM-EuCd2As2, but we hardly observe spin-phonon coupling and find negligible DCP values due to almost zero net magnetization. Our results contribute to the understanding of the phonon dynamics and the interplay between topology and magnetism in FM-EuCd2As2, through helical light and external magnetic fields. This lays the foundation for utilizing state-of-the-art Weyl systems for applications in thermoelectrics, phononic devices, and topological quantum computing.

cond-mat.mtrl-sci↗

arXiv2026

Graduate Training in Quantum Information Science and Engineering: Lessons, Challenges, and a Roadmap from the NSF Research Traineeship Programs

Since 2019, eighteen NSF Research Traineeship (NRT) awards in quantum information science and engineering (QISE) and adjacent fields have been funded, constituting the largest NSF-coordinated investment in graduate QISE training in the United States. Synthesizing lessons from our programs, we work through the central tensions that every QISE graduate program must negotiate: between depth in a home discipline and breadth across the field, between structured instruction and open-ended experiential and hands-on learning, and between training individual specialists and cultivating teams that collectively cover all areas of QISE. We describe the structural and pedagogical innovations the NRT programs have developed in response, assess what is working and what remains unresolved, and sketch 12 open problems the community will need to address as QISE graduate education scales beyond the well-resourced research universities where it has up till now been mainly concentrated. Eight concrete recommendations follow: (1) adopt the startup model of team-based training as an organizing philosophy; (2) invest immediately in sensing and communication curriculum development; (3) build student agency into program governance, not just activities; (4) establish structural mechanisms for industrial engagement rather than depending on goodwill; (5) design for sustainability from year one; (6) develop graduate-level textbooks spanning all three QISE pillars: computing, sensing, and communications; (7) establish shared outcome assessment instruments across programs; and (8) develop structured mechanisms for faculty professional development in QISE.

physics.ed-ph↗

arXiv2026

High-dimensional quantum communication with scalable photonic entanglement in time and frequency

High-dimensional photonic entanglement holds significant promise for advancing quantum communication, computation, and metrology. For example, large-alphabet quantum communication protocols are known to benefit from enhanced noise resilience and information capacity via multi-bit time-bin encoding. Yet, characterizing high-dimensional entangled states is challenging, as full state tomography becomes prohibitively costly and often requires unrealizable measurements. Here, we demonstrate a scan-free method to characterize high-dimensional entanglement in the time-frequency domain. Our reconstruction achieves a record $5.70\pm0.07$ ebits and a fidelity of $65.4\pm0.4\%$ with the maximally entangled state of local dimension $1021$, certifying the presence of $668$-dimensional entanglement. We further prove the attainability of a secure key rate of $15.6$ kB/s in a composable finite-size, entanglement-based protocol, and show that in continuous operation, the setup can quickly approach asymptotic key rates. Using commercial telecom components and state-of-the-art low-jitter single-photon detectors, our scalable architecture offers a practical path towards high-rate, noise-resilient quantum communication testbeds.

quant-ph↗

arXiv2026

GKP-inspired high-dimensional superdense coding with energy-time entanglement

Superdense coding, the application of entanglement to boost classical communication capacity, is a cornerstone of quantum communication. In this paper, we propose a high-dimensional superdense coding protocol using energy-time entangled states. These states are biphoton frequency combs, an example of entangled time-frequency Gottesman-Kitaev-Preskill (TFGKP) states or time-frequency grid states. Inspired by GKP codes, our protocol involves discretizing the continuous time and frequency degrees of freedom and encoding information by time-frequency displacements. This approach leverages the inherently large Hilbert space found in quantum frequency combs, with resilience against both temporal and spectral errors. In addition to describing the theoretical structure of the protocol, we propose an experimental implementation using standard telecommunication components, time-resolving single-photon detectors and a frequency beamsplitter. We also analyze the effect of experimental noise and errors on the channel capacity of the protocol. We demonstrate that for realistic experimental parameters, contemporary technologies satisfy the prerequisites for superdense coding with biphoton frequency combs, achieving a transmission rate of approximately 8.91 bits per transmitted photon (equivalent to 481 distinguishable messages with asymptotically vanishing errors). This more than doubles the previously highest transmission rate of 4 bits achieved by the Kwiat-Weinfurter scheme, while also having competitive optical loss. Furthermore, our results beat the rate achievable using a single-photon frequency comb with identical parameters by 4.6 times. Our protocol thus represents an experimentally feasible application of time-frequency grid states to entanglement-assisted communication, contributing to the active fields of continuous-variable and high-dimensional quantum information.

quant-ph↗

arXiv2025

Experimental high-dimensional entanglement certification and quantum steering with time-energy measurements

High-dimensional entanglement provides unique ways of transcending the limitations of current approaches in quantum information processing, quantum communications based on qubits. The generation of time-frequency qudit states offer significantly increased quantum capacities while keeping the number of photons constant, but pose significant challenges regarding the possible measurements for certification of entanglement. Here, we develop a new scheme and experimentally demonstrate the certification of 24-dimensional entanglement and a 9-dimensional quantum steering. We then subject our photon-pairs to dispersion conditions equivalent to the transmission through 600-km of fiber and still certify 21-dimensional entanglement. Furthermore, we use a steering inequality to prove 7-dimensional entanglement in a semi-device independent manner, proving that large chromatic dispersion is not an obstacle in distributing and certifying high-dimensional entanglement and quantum steering. Our approach, leveraging intrinsic large-alphabet nature of telecom-band photons, enables scalable, commercially viable, and field-deployable entangled and steerable quantum sources, providing a pathway towards fully scalable quantum information processer and high-dimensional quantum communication networks.

quant-ph↗

arXiv2025

Quantum teleportation of an elemental silicon nanophotonic CNOT gate

Large-scale quantum computers possess the capacity to effectively tackle practical problems that can be insurmountable for classical computers. The main challenge in building these quantum computers is to realize scalable modules for remote qubits and entanglement. By assembling small, specialized parts into a larger architecture, the modular approach mitigates complexity and uncertainty. Such a distributed architecture requires non-local quantum gate operations between remote qubits. An essential method for implementing such operations, known as quantum gate teleportation, requires only local operations, classical communication, and shared entanglement. Till today, the quantum gate teleportation using a photonic chip has remained elusive. Here we experimentally demonstrate the quantum teleportation of an on-chip controlled-NOT (CNOT) gate, assisted with the scalable silicon chip platform, high-fidelity local quantum logic gates, linear optical components, post-selected entanglement, and coincidence measurements from photonic qubits. First, we measure and characterize our teleported chip-scale CNOT gate with an average truth table fidelity of 93.1 +- 0.3%. Second, for different input polarization states, we obtain an average quantum state fidelity of 87.0 +- 2.2% with our teleported on-chip CNOT gate. Third, we use our non-local CNOT gate for remote entanglement creation of four Bell states, with an average quantum state fidelity of 86.2 +- 0.8%. Fourthly, we fully characterize our teleported on-chip CNOT gate with a quantum process fidelity 83.1 +- 2.0%, and an average non-local CNOT gate fidelity of 86.5 +- 2.2%. Our teleported photonic on-chip quantum logic gate could be extended both to multiple qubits and chip-scale modules towards fault-tolerant and large-scale distributed quantum computation.

quant-ph↗

arXiv2025

Bistable random momentum transfer in a linear on-chip resonator

Optical switches and bifurcation rely on the nonlinear response of materials. Here, we demonstrate linear temporal bifurcation responses in a passive multimode microresonator, with strongly coupled chaotic and whispering gallery modes or WGMs. In microdisks, the chaotic modes exhibit broadband transfer within the deformed cavities, but their transient response is less explored and yields a random output of the analog signal distributed uniformly from 0 to 1. Here, we build chaotic states by perturbing the multi-mode microring resonators with densely packed silicon nanocrystals on the waveguide surface. In vivo measurements reveal random and digitized output that ONLY populates around 0 and 1 intensity levels. The bus waveguide mode couples firstly to chaotic modes, then either dissipates or tunnels into stable WGMs. This binary pathway generates high-contrast, digitized outputs. The fully passive device enables real-time conversion of periodic clock signals into binary outputs with contrasts exceeding 12.3 dB, data rates of up to 100 Mbits per second, and 20dB dynamic range.

physics.optics↗

arXiv2025

Reducing classical communication costs in multiplexed quantum repeaters using hardware-aware quasi-local policies

Future quantum networks will have nodes equipped with multiple quantum memories, allowing for multiplexing and entanglement distillation strategies in order to increase fidelities and reduce waiting times for end-to-end entanglement distribution. In this work, we introduce \textit{quasi-local} policies for multiplexed quantum repeater chains. In fully-local policies, nodes make decisions based only on knowledge of their own states. In our quasi-local policies, nodes have increased knowledge of the state of the repeater chain, but not necessarily full, global knowledge. Our policies exploit the observation that for most decisions the nodes have to make, they only need to have information about the connected region of the chain they belong to, and not the entire chain. In this way, we not only obtain improved performance over local policies, but we reduce the classical communication (CC) costs inherent to global-knowledge policies. Our policies also outperform the well-known and widely studied nested purification and doubling swapping policy in practically relevant parameter regimes. We also carefully examine the role of entanglement distillation. Via analytical and numerical results, we identify the parameter regimes in which distillation makes sense and is useful. In these regimes, we also address the question: "Should we distill before swapping, or vice versa?" Finally, to provide further practical guidance, we propose an experimental implementation of a multiplexing-based repeater chain, and experimentally demonstrate the key element, a high-dimensional biphoton frequency comb. We then evaluate the anticipated performance of our multiplexing-based policies in such a real-world network through simulation results for two concrete memory platforms, namely rare-earth ions and diamond vacancies.

quant-ph↗

arXiv2025

Mapping ultrafast timing jitter in dispersion-managed 89 GHz frequency microcombs via self-heterodyne linear interferometry

Laser frequency microcombs provide equidistant coherent frequency markers over a broad spectrum, enabling new frontiers in chip-scale frequency metrology, laser spectroscopy, dense optical communications, precision distance metrology and astronomy. Here we demonstrate thermally stabilized frequency microcomb formation in dispersion-managed microresonators at the different mode-locking states featured with the negligible center frequency shift and broad frequency bandwidth. Subsequently, femtosecond timing jitter in the microcombs are characterized, supported by precision metrology on the timing phase, relative intensity noise and instantaneous linewidth. We contrast the fundamental noise for a range of 89 GHz microcomb states, from soliton crystals to multiple solitons and single-soliton regimes, determined by pump-resonance detuning. For the single-soliton state, we report a close-to-shot-noise-limited relative intensity noise of -153.2 dB/Hz and a quantum-noise-limited timing jitter power spectral density of 0.4 as2/Hz, at 100 kHz offset frequency. This is enabled by a self-heterodyne linear interferometer with 94.2 zs/Hz1/2 timing resolution, 50.6 mHz/Hz1/2 RF frequency resolution, and 6.7 uV/Hz frequency discrimination sensitivity. We achieve an integrated timing jitter at 1.7 fs, integrated from 10 kHz to 1 MHz. Measuring and understanding the fundamental noise parameters in these high-clock-rate frequency microcombs are essential to advance soliton physics and precision microwave-optical clockwork.

physics.optics↗

arXiv2025

Near-energy-free Photonic Fourier Transformation for Convolution Operation Acceler

Convolutional operations are computationally intensive in artificial intelligence services, and their overhead in electronic hardware limits machine learning scaling. Here, we introduce a photonic joint transform correlator (pJTC) using a near-energy-free on-chip Fourier transformation to accelerate convolution operations. The pJTC reduces computational complexity for both convolution and cross-correlation from O(N4) to O(N2), where N2 is the input data size. Demonstrating functional Fourier transforms and convolution, this pJTC achieves 98.0% accuracy on an exemplary MNIST inference task. Furthermore, a wavelength-multiplexed pJTC architecture shows potential for high throughput and energy efficiency, reaching 305 TOPS/W and 40.2 TOPS/mm2, based on currently available foundry processes. An efficient, compact, and low-latency convolution accelerator promises to advance next-generation AI capabilities across edge demands, high-performance computing, and cloud services.

physics.optics↗

arXiv2025

Recent advances in high-dimensional mode-locked quantum frequency combs

High-dimensional entanglement in qudit states offers a promising pathway towards the realization of practical, large-scale quantum systems that are highly controllable. These systems can be leveraged for various applications, including advanced quantum information processing, secure communications, computation, and metrology. In this context, quantum frequency combs have a crucial role as they inherently support multiple modes in both temporal and frequency domains, while preserving a single spatial mode. The multiple temporal and frequency modes of quantum frequency combs facilitate the generation, characterization, and control of high-dimensional time-frequency entanglement in extensive quantum systems. In this review article, we provide an overview of recent technological advancements in high-dimensional energy-time entangled quantum frequency combs. We explore how these time-frequency qudits, achieved using scalable telecommunications-wavelength components, can empower the creation of large-scale quantum states. Advances in quantum frequency combs can unlock new capabilities and versatility for promising developments in quantum science and technology.

quant-ph↗

arXiv2024

Photophysics of O-band and transition metal color centers in monolithic silicon for quantum communications

Color centers in the O-band (1260-1360 nm) are critical for realizing long-coherence quantum network nodes in memory-assisted quantum communications. However, only a limited number of O-band color centers have been explored in silicon hosts as spin-photon interfaces. This study explores and compares two promising O-band defects in silicon: T centers and $^*$Cu (transition metal) color centers. During T center formation, we observed the formation and dissolution of various defects, including the copper-silver-related defect with a doublet line around 1312 nm ($^*$Cu$^{0}_{n}$), near the optical fiber zero dispersion wavelength. We then investigate the photophysics of both T and $^*$Cu centers, focusing on their emission spectra and spin properties to assess their potential for high-fidelity spin-photon interfaces. Additionally, we report a 25\% broadening of the $^*$Cu$^{0}_{0}$ line under a 0.5 T magnetic field, potentially linked to spin degeneracy, suggesting that this defect may provide a promising alternative to T centers for spin-photon interfaces.

quant-ph↗

arXiv2024

Remote picometric acoustic sensing via ultrastable laser interferometry

Acoustic detection has many applications across science and technology, from medical to imaging and communications. However, most acoustic sensors have a common limitation in that the detection must be near the acoustic source. Alternatively laser interferometry with picometer-scale motional displacement detection can rapidly and precisely measure sound induced minute vibrations on remote surfaces. Here we demonstrate the feasibility of sound detection up to 100 kHz at remote sites with ~ 60 m of optical path length via laser homodyne interferometry. Based on our ultrastable Hz-linewidth laser with 10-15 fractional stability, our laser interferometer achieves 0.5 pm/Hz1/2 displacement sensitivity near 10 kHz, bounded only by laser frequency noise over 10 kHz. Between 140 Hz to 15 kHz, we achieve a homodyne acoustic sensing sensitivity of sub-nm/Pa across our conversational frequency overtones. The minimal sound pressure detectable over 60 m of optical path length is ~ 2 mPa, with dynamic ranges over 100 dB. With the demonstrated standoff picometric distance metrology, we successfully detected and reconstructed musical scores of normal conversational volumes with high fidelity. The acoustic detection via this precision laser interferometer could be applied to selective area sound sensing for remote acoustic metrology, optomechanical vibrational motion sensing and ultrasensitive optical microphones at the laser frequency noise limits.

physics.optics↗

arXiv2024

Spatio-temporal breather dynamics in microcomb soliton crystals

Solitons, the distinct balance between nonlinearity and dispersion, provide a route toward ultrafast electromagnetic pulse shaping, high-harmonic generation, real-time image processing, and RF photonic communications. Here we newly explore and observe the spatio-temporal breather dynamics of optical soliton crystals in frequency microcombs, examining spatial breathers, chaos transitions, and dynamical deterministic switching in nonlinear measurements and theory. To understand the breather solitons, we describe their dynamical routes and two example transitional maps of the ensemble spatial breathers, with and without chaos initiation. We elucidate the physical mechanisms of the breather dynamics in the soliton crystal microcombs, in the interaction plane limit cycles and in the domain-wall understanding with parity symmetry breaking from third order dispersion. We present maps of the accessible nonlinear regions, the breather frequency dependences on third order dispersion and avoided mode crossing strengths, and the transition between the collective breather spatiotemporal states. Our range of measurements matches well with our first-principles theory and nonlinear modeling. To image these soliton ensembles and their breathers, we further constructed panoramic temporal imaging for simultaneous fast and slow axis two dimensional mapping of the breathers. In the phase differential sampling, we present two dimensional evolution maps of soliton crystal breathers, including with defects, in both stable breathers and breathers with drift. Our fundamental studies contribute to the understanding of nonlinear dynamics in soliton crystal complexes, their spatiotemporal dependences, and their stability-existence zones.

nlin.PS↗

arXiv2024

Stochastic modeling of superconducting qudits in the dispersive regime

The field of superconducting quantum computing, based on Josephson junctions, has recently seen remarkable strides in scaling the number of logical qubits. In particular, the fidelities of one- and two-qubit gates have reached the breakeven point with the novel error mitigation and correction methods. Parallel to these advances is the effort to expand the Hilbert space within a single junction or device by employing high-dimensional qubits, otherwise known as qudits. Research has demonstrated the possibility of driving higher-order transitions in a transmon or designing innovative multimode superconducting circuits, termed multimons. These advances can significantly expand the computational basis while simplifying the interconnects in a large-scale quantum processor. In this work we extend the measurement theory of a conventional superconducting qubit to that of a qudit, focusing on modeling the dispersive quadrature measurement in an open quantum system. Under the Markov assumption, the qudit Lindblad and stochastic master equations are formulated and analyzed; in addition, both the ensemble-averaged and the quantum-jump approach of decoherence analysis are detailed with analytical and numerical comparisons. We verify our stochastic model with a series of experimental results on a transmon-type qutrit, verifying the validity of our high-dimensional formalism.

quant-ph↗

arXiv2024

Block-MDS QC-LDPC Codes for Information Reconciliation in Key Distribution

Quantum key distribution (QKD) is a popular protocol that provides information theoretically secure keys to multiple parties. Two important post-processing steps of QKD are 1) the information reconciliation (IR) step, where parties reconcile mismatches in generated keys through classical communication, and 2) the privacy amplification (PA) step, where parties distill their common key into a new secure key that the adversary has little to no information about. In general, these two steps have been abstracted as two distinct problems. In this work, we consider a new technique of performing the IR and PA steps jointly through sampling that relaxes the requirement on the IR step, allowing for more success in key creation. We provide a novel LDPC code construction known as Block-MDS QC-LDPC codes that can utilize the relaxed requirement by creating LDPC codes with pre-defined sub-matrices of full-rank. We demonstrate through simulations that our technique of sampling can provide notable gains in successfully creating secret keys.

cs.IT↗

arXiv2023

Isotropic gap formation, localization, and waveguiding in mesoscale Yukawa-potential amorphous structures

Amorphous photonic structures are mesoscopic optical structures described by electrical permittivity distributions with underlying spatial randomness. They offer a unique platform for studying a broad set of electromagnetic phenomena, including transverse Anderson localization, enhanced wave transport, and suppressed diffusion in random media. Despite this, at a more practical level, there is insufficient work on both understanding the nature of optical transport and the conditions conducive to vector-wave localization in these planar structures, as well as their potential applications to photonic nanodevices. In this study, we fill this gap by investigating experimentally and theoretically the characteristics of optical transport in a class of amorphous photonic structures and by demonstrating their use to some basic waveguiding nanostructures. We demonstrate that these 2-D structures have unique isotropic and asymmetric band gaps for in-plane propagation, controlled from first principles by varying the scattering strength and whose properties are elucidated by establishing an analogy between photon and carrier transport in amorphous semiconductors. We further observe Urbach band tails in these random structures and uncover their relation to frequency- and disorder-dependent Anderson-like localized modes through the modified Ioffe-Regel criterion and their mean free path - localization length character. Finally, we illustrate that our amorphous structures can serve as a versatile platform in which photonic devices such as disorder-localized waveguides can be readily implemented.

physics.optics↗

arXiv2023

Single site-controlled inverted pyramidal InGaAs QD-nanocavity operating at the onset of the strong coupling regime

Precise positioning of single site-controlled inverted pyramidal InGaAs QD at the antinode of a GaAs photonic crystal cavity with nanometer-scale accuracy holds unique advantages compared to self-assembled QDs and offers great promise for practical on-chip photonic quantum information processing. However, the strong coupling regime in this geometry has not yet been achieved due to the low cavity Q-factor based on the (111)B-oriented membrane structures. Here, we reveal the onset of phonon-mediated coherent exciton-photon interaction on our tailored single site-controlled InGaAs QD - photonic crystal cavity. Our results present a Rabi-like oscillation of luminescence intensity between excitonic and photonic components correlated with their energy splitting pronounced at small detuning. Such Rabi-like oscillation is well reproduced by modeling the coherent exchange of the exciton-photon population. The modeling further reveals an oscillatory two-time covariance at QD-cavity resonance, which indicates that the system operates at the onset of the strong coupling regime. Moreover, by using the cavity mode as a probe of the virtual state of the QD induced by phonon scattering, it reveals an increase in phonon scattering rates near the QD-cavity resonance and asymmetric phonon emission and absorption rate even around 50 K.

cond-mat.mes-hall↗