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 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]

Experimental optimal verification of three-dimensional entanglement on a silicon chip

As a crucial step toward practical quantum technologies is to verify that these devices work reliably with an optimal strategy, Lijun and the team present experimentally implement an optimal quantum verification strategy on a three-dimensional maximally entangled state using local projective measurements on a silicon photonic chip. 

A 95% confidence is achieved from 1190 copies to verify the target quantum state. The obtained scaling of infidelity as a function of the number of copies is −0.5497 ± 0.0002, exceeding the standard quantum limit of −0.5 with 248 standard deviations.

See New J. Phys. 24 095002 for details.   [2022-09-07]

Realizing an Entanglement-Based Multiuser Quantum Network with Integrated Photonics

Wenjun et al. develop an energy-time entanglement-based dense wavelength division multiplexed network based on an integrated silicon nitride microring resonator. 

Specifically, six pairs of photons are selected to form a fully and simultaneously connected four-user quantum network. The observed quantum interference visibilities are well above the classical limits among all users. Each pair of users perform the BBM92 protocol for quantum key distribution. Our results pave the way for realizing large-scale quantum networks with integrated photonic architecture.

See Phys. Rev. Applied 18, 024059 [Editors' Suggestion]  for details.   [2022-08-22]

Advances in Chip-Scale Quantum Photonic Technologies

With quantum photonic system's complexity and functionality scaling up, the requirements for stability, programmability, and manufacturability will be in high demand. Integrated photonics has overwhelming dominance in terms of density and performance.

Recently, Liangliang Lu et al. present the recent advances in components that constitute quantum photonic systems on silicon photonics platform, including sources, modulators, and detectors are reviewed. Burgeoning quantum photonics applications, such as multi-dimensional, multi-photon QIP and integrated quantum key distribution are highlighted.

See Advanced Quantum Technologies 4: 2100068 for details.   [2021-11-09]

Heterogeneously integrated, superconducting silicon-photonic platform for measurement-device-independent quantum key distribution

Xiaodong and Peiyu Zhang, toghether with our collaborators Renyou Ge, Liangliang Lu, Guanglong He, Qi Chen et al. realize a heterogeneously integrated, superconducting silicon-photonic chip, and perform the first optimal Bell-state measurement (BSM) of time-bin encoded qubits. 

Together with the time-multiplexed technique, we obtain a secure key rate of 6.166 kbps over 24.0 dB loss with a 125-MHz clock rate, which is comparable to the state-of-the-art MDI-QKD experimental results with a GHz clock rate.

See Advanced Photonics 3(5): 055002 for details.   [2021-10-31]