Seminar: Imaging and time-stamping optical photons with sub-nanosecond resolution for quantum imaging, astrophysics and other applications

Prof. Andrei Nomerotski presents ultra-fast cameras utilizing back-illuminated silicon sensors and Timepix ASICs, achieving nanosecond-resolution and single-photon detection for quantum imaging, neutron detection, and ion imaging applications. He reviews entanglement-enhanced interferometry to overcome limitations in Michelson and Hanbury Brown–Twiss (HBT) interferometry, and proposes a novel two-photon amplitude interferometry technique requiring picosecond timestamping and spectral binning, with resolution products approaching the Heisenberg Uncertainty Principle limit. He also showcases recent experimental results and outlines future directions for the imaging technology.   [2025-07-10]

Quantum Teleportation from Telecom Photons to Erbium-Ion Ensembles

To realize a quantum internet, the distribution of quantum states via quantum teleportation with quantum memories is a key ingredient. Being compatible with existing fiber networks, entangled photons and quantum memories at telecom wavelength are of central interest for such a scalable quantum network. 

Here, Yuyang, Qian and Wenyi et al. demonstrate quantum teleportation from a telecom-wavelength photonic qubit to a solid-state quantum memory based on erbium-ion ensembles, which have a native optical transition at 1.5 μ⁢m telecom C band. To accomplish this, we use chip-scale silicon nitride microresonators to generate entangled photons with narrow linewidth, compatible with the quantum memory. 

See Phys. Rev. Lett. 135, 010804 for details.   [2025-07-02]

A measurement-device-independent quantum key distribution network using optical frequency comb

Quantum key distribution (QKD), which promises secure key exchange between two remote parties, is now moving toward the realization of scalable and secure QKD networks (QNs).

Recently, Wenhan & Xiaodong et al. experimentally demonstrate a fully connected multi-user QKD network by combining the MDI-QKD protocol with integrated optical frequency combs, achieving an average secure key rate of 267 bits per second for about 30 dB of link attenuation per user pair—more than three orders of magnitude higher than previous entanglement-based works. More importantly, we realize communication between two different pairs of users simultaneously.

See npj Quantum Information 11, 97 for details.   [2025-06-09]

Ten-channel Hong–Ou–Mandel interference between independent optical combs

The fabrication-induced frequency mismatches for multiple independent frequency combs is critical in measurement-device-independent quantum key distribution, which requires high visibility of Hong–Ou–Mandel interference between multiple frequency channels. 

Here, Wenhan & Yang Hu et al. experimentally demonstrate two independent dissipative Kerr soliton (DKS) frequency combs with 10 spectrally aligned lines without any frequency locking system. The visibility for individual comb-line pairs reaches up to 46.72% ± 0.63% via precision frequency translation, establishing a foundation for deploying DKS combs in multi-user quantum networks.

See Chin. Opt. Lett. 23, 042701 for details.   [2025-04-26]

Experimental Measurement-Device-Independent Quantum Cryptographic Conferencing

Quantum cryptographic conferencing (QCC) allows sharing secret keys among multiple distant users and plays a crucial role in quantum networks. Because of the fragility and low generation rate of genuine multipartite entangled states required in QCC, realizing and extending QCC with the entanglement-based protocol is challenging. 

Yifeng, Yufeng and the team experimentally realize the three-user MDI QCC protocol with four-intensity decoy-state method. Our work demonstrates the experimental feasibility of the MDI QCC, which lays the foundation for the future realization of quantum networks with multipartite communication tasks.

See Phys. Rev. Lett. 134, 040802 for details.   [2025-01-28]

Entangling Independent Particles by Path Identity

Traditionally, entanglement is achieved through local interactions or via entanglement swapping. However, the precise requirements enabling the generation of quantum entanglement without traditional local interactions remain less explored. 

Kai Wang and Zhaohua in collaboration with the group of Mario Krenn demonstrate that independent particles can be entangled without the need for direct interaction, prior established entanglement, or Bell-state measurements, by exploiting the indistinguishability of the origins of photon pairs.

See Phys. Rev. Lett. 133, 233601 for details.   [2024-12-10]

Discrete and Parallel Frequency-Bin Entanglement Generation from Quantum Frequency Comb

Quantum frequency combs (QFCs) generated in integrated nonlinear microresonators can produce multiple frequency modes with narrow linewidth, and photons' frequency degree of freedom is promising to realize large-scale quantum information processing.

Chi Lu et al. utilize polarization-entangled QFCs to generate discrete frequency-bin entangled states. Fourteen pairs of polarization-entangled photons with different frequencies are simultaneously transformed into frequency-bin entangled states.

See Advanced Quantum Technologies 8, 2400229 for details.   [2024-11-06]

Observation of quantum nonlocality in Greenberger-Horne-Zeilinger entanglement on a silicon chip

Entangled states with multiple particles are of crucial importance in fundamental tests of quantum physics as well as in many quantum information tasks. One of the archetypal multipartite quantum states, Greenberger-Horne-Zeilinger (GHZ) state, allows one to observe the striking conflict of quantum physics to local realism in the so-called all-versus-nothing way.

Leizhen and Bochi et al. demonstrate an integrated photonic chip capable of generating and manipulating the four-photon GHZ state. Our work paves the way to perform fundamental tests of quantum physics with complex integrated quantum devices.

See Opt. Express 32, 14904-14913 for detials.   [2024-04-24]

Polarization-entangled quantum frequency comb from a silicon nitride microring resonator

Integrated microresonator facilitates the realization of quantum frequency comb (QFC), which provides a large number of discrete frequency modes with broadband spectral range and narrow linewidth.

Wenjun and the team demonstrate a broadband polarization-entangled quantum frequency comb by combining an integrated silicon-nitride microresonator with a Sagnac interferometer. Our source provides 22 polarization-entangled photon pairs with frequency covering the whole telecom C-band. The entanglement fidelities for all 22 pairs are above 81%, including 17 pairs with fidelities higher than 90%.

See Phys. Rev. Applied 20, 064032 for details.   [2023-12-20]

Quantum storage of entangled photons at telecom wavelengths in a crystal

Quantum storage and distribution of entanglement are the key ingredients for realizing a global quantum internet. Compatible with existing fiber networks, telecom-wavelength entangled photons and corresponding quantum memories are of central interest.

Combining the natural narrow linewidth of the entangled photons generated from an integrated photonic chip and long storage time of 167Er3+ ions, Minghao, Wenyi and colleagues achieve a quantum storage time of 1.936 μs, more than 387 times longer than in previous works. Successful storage of entanglement in the crystal is certified using entanglement witness measurements. 

See Nat Commun 14, 6995 for details.   [2023-11-01]

On-Chip Generation and Collectively Coherent Control of the Superposition of the Whole Family of Dicke States

Dicke state is an important class of genuinely entangled state, which has been systematically studied in the light-matter interactions, quantum state engineering, and quantum metrology. 

By using a silicon photonic chip, Leizhen et al. report the generation and collectively coherent control of the entire family of four-photon Dicke states, i.e., with arbitrary excitations. We generate four entangled photons from two microresonators and coherently control them in a linear-optic quantum circuit, in which the nonlinear and linear processing are achieved in a chip-scale device.

See Phys. Rev. Lett. 130, 223601 for details.   [2023-06-01]

Multiphoton non-local quantum interference controlled by an undetected photon

Collaborating with the group of Mario Krenn, Kaiyi, Kai Wang et al. control the non-local multipartite quantum interference with a photon that we never detect, which does not require quantum entanglement, though entanglement is typically considered to be essential for creating non-local quantum interference. 

We harness the superposition of the physical origin of a four-photon product state, which leads to constructive and destructive interference with the photons’ mere existence. With the intrinsic indistinguishability in the generation process of photons, we realize four-photon frustrated quantum interference.

See Nat Commun 14, 1480 for details.   [2023-03-17]

Interaction-free, single-pixel quantum imaging with undetected photons

Recently, Yiquan et al. propose and experimentally demonstrate interaction-free, single-pixel quantum imaging of a structured object with undetected photons by embedding a single-photon Michelson interferometer into a nonlinear interferometer based on induced coherence and harnessing single-pixel imaging technique.

We push the capability of quantum imaging to the extreme point in which no interaction is required between object and photons and the detection requirement is greatly reduced. Our work paves the path for applications in characterizing delicate samples with single-pixel imaging at silicon-detectable wavelengths.

See npj Quantum Inf 9, 2 for details.   [2023-01-06]

Controlling wave-particle duality with entanglement between single-photon and Bell states

Wave-particle duality and entanglement are two fundamental characteristics of quantum mechanics. All previous works on experimental investigations in wave-particle properties of single photons (or single particles in general) showed that a well-defined interferometer setting determines a well-defined property of single photons. 

Kai Wang with our collaborator take a conceptual step forward and control the wave-particle property of single photons with a Bell state. We experimentally test the complementarity principle in a scenario in which the setting of the interferometer is not defined at any instance of the experiment, not even in principle. 

See Phys. Rev. A 106, 053715 for details.   [2022-11-30]

Minimum detection efficiency for testing a multi-particle Bell inequality

Wenchao et al. generalize two-particle Eberhard's inequality to the n-particle systems and derive a Bell-type inequality for multi-particle systems, which significantly relaxes the threshold of sampling efficiency (including the collection and detection efficiencies) for the photonic system. 

Furthermore, an experimental proposal to achieve a multi-partite Bell test without the fair sampling assumption is presented for the case of three particles. For any given value of the sampling efficiency, we give the optimal configurations for actual implementation, the optimal state, the maximum background noise that the system can tolerate, and the lowest fidelity of the quantum state.

See New J. Phys. 24 113031 for details.   [2022-11-18]