[Paper Review] Observation of nonlocal quantum interference between the origins of a four-photon state in a silicon chip

Lan‐Tian Feng, Ming Zhang+7 more|arXiv (Cornell University)|Mar 26, 2021

Quantum Information and Cryptography30 references4 citations

TL;DR

This study demonstrates nonlocal quantum interference between two distinct spatial origins of a four-photon state on a silicon photonic chip, using four integrated spiral waveguides to generate photon pairs via spontaneous four-wave mixing. By tuning a phase, coherent suppression and revival of the 4-photon state are achieved, revealing nonlocal effects without explicit entanglement, highlighting a new platform for quantum nonlocality and integrated quantum technologies.

ABSTRACT

Quantum mechanically, multiple particles can jointly be in a coherent superposition of two or more different states at the same time. This property is called quantum entanglement, and gives rise to characteristic nonlocal interference and stays at the heart of quantum information process. Here, rather than interference of different intrinsic properties of particles, we experimentally demonstrated coherent superposition of two different birthplaces of a four-photon state. The quantum state is created in four probabilistic photon-pair sources, two combinations of which can create photon quadruplets. Coherent elimination and revival of distributed 4-photons can be fully controlled by tuning a phase. The stringent coherence requirements are met by using a silicon-based integrated photonic chip that contains four spiral waveguides for producing photon pairs via spontaneous four-wave mixing. The experiment gives rise to peculiar nonlocal phenomena without any obvious involvement of entanglement. Besides several potential applications that exploit the new on-chip technology, it opens up the possibility for fundamental studies on nonlocality with spatially separated locations.

Motivation & Objective

• To explore nonlocal quantum phenomena arising from the coherent superposition of spatially separated sources of a four-photon state.
• To demonstrate control over the generation of 4-photon states through phase tuning in a compact, integrated photonic platform.
• To investigate nonlocal interference effects without relying on traditional entanglement-based mechanisms.
• To develop a scalable on-chip solution for generating and manipulating multiphoton quantum states with high coherence.

Proposed method

• Utilized a silicon-based integrated photonic chip with four spiral waveguides to enable spontaneous four-wave mixing for probabilistic photon-pair generation.
• Engineered two independent pairs of photon-pair sources to create four-photon states via two distinct source combinations.
• Implemented precise phase control across the chip to coherently manipulate the interference between the two source pathways.
• Measured the output state population to observe coherent suppression and revival of the 4-photon state as a function of phase tuning.
• Ensured stringent coherence requirements through the high stability and low loss of the integrated waveguide architecture.
• Used the interference pattern to probe nonlocal quantum behavior arising from spatially separated origins of the same quantum state.

Experimental results

Research questions

• RQ1 Can nonlocal quantum interference be observed between two distinct spatial origins of a four-photon state without relying on entanglement?
• RQ2 To what extent can the generation of a 4-photon state be coherently controlled via phase tuning in an integrated photonic platform?
• RQ3 What are the observable signatures of coherent superposition of source locations in a multiphoton quantum state?
• RQ4 How does the integrated silicon chip architecture support the stringent coherence requirements for such nonlocal quantum effects?

Key findings

• Coherent suppression and revival of the four-photon state were experimentally observed by tuning the relative phase between the two source pathways.
• The interference pattern demonstrated clear nonlocal behavior, with the outcome depending on the phase difference between spatially separated sources.
• The system exhibited high visibility in the interference fringes, confirming the coherence of the superposition between distinct birthplaces.
• The absence of explicit entanglement in the state's construction highlights a novel mechanism for nonlocal quantum effects.
• The silicon photonic chip enabled stable, low-loss operation with precise phase control, essential for observing the effect.
• The results open new pathways for fundamental studies of nonlocality and integrated quantum information processing.