Generating photons for communication between quantum processors

New technique provides a means of interconnection between quantum processors.


Realizing a completely associated organization of quantum processors requires the capacity to distribute quantum entanglement. This can be accomplished for distant processing nodes by creating, routing, and catching spatially entangled inherent photons.

Conventional approaches for generating such photons in optical systems typically use spontaneous parametric down-conversion in conjunction with arrays of beamsplitters and photodetectors for postselection. However, the stochastic nature of these approaches limits their utility in quantum information processing applications.

In a new study, MIT scientists used superconducting qubits connected to a microwave transmission line to generate spatially entangled itineran photons for communication between quantum processors.

William Oliver, an associate professor of electrical engineering and computer science, MIT Lincoln Laboratory fellow, director of the Center for Quantum Engineering, and associate director of the Research Laboratory of Electronics said, “Superconducting qubits are a leading technology today, but they generally support only local interactions (nearest-neighbor or qubits very close by). The question is how to connect to qubits that are at distant locations. We need quantum interconnects, ideally based on microwave waveguides that can guide quantum information from one location to another.”

The development is a significant advance toward accomplishing the interconnections that would allow a modular quantum computing system to perform tasks at rates exponentially quicker than classical computers can achieve.

Oliver said, “We generate the entangled photons on demand using the qubits and then release the entangled state to the waveguide with very high efficiency, essentially unity.”

The work presents another architecture for creating photons spatially entangled in a basic way, utilizing just a waveguide and a couple of qubits, which go about as the photonic emitters. The photons’ entanglement can then be transferred into the processors for use in quantum communication or interconnection protocols.

In this study, scientists demonstrated the photon generation ability of the waveguide quantum electrodynamics architecture. They have shown that qubits can be used as quantum emitters for the waveguide. 

Also, scientists found that quantum interference between the photons emitted into the waveguide generates entangled, itinerant photons that travel in opposite directions and can be used for long-distance communication between quantum processors.

Generating spatially entangled photons in optical systems is typically accomplished using spontaneous parametric down-conversion and photodetectors. Still, the generated entanglement achieved that way is generally random and less useful in enabling on-demand communication of quantum information in a distributed system.

Oliver said“Modularity is a key concept of an extensible system. Our goal here is to demonstrate the elements of quantum interconnects that should be useful in future quantum processors.”

Journal Reference:
  1. B. Kannan et al. Generating spatially entangled itinerant photons with waveguide quantum electrodynamics. DOI: 10.1126/sciadv.abb8780


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