Researchers from the Massachusetts Institute of Technology (MIT) have developed a quantum computing architecture that can enable extensible, high-fidelity communication between superconducting quantum processors.

The MIT researchers demonstrated step one in their work, the deterministic emission of single photons, or information carriers, in a user-specified direction, ensuring quantum information flows in the correct direction more than 96% of the time.

Linking several of these modules enables a larger network of quantum processors that interconnect with one another despite their physical separation on a computer chip.

“The ability to communicate between smaller subsystems will enable a modular architecture for quantum processors, and this may be a simpler way of scaling to larger system sizes compared to the brute-force approach of using a single large and complicated chip,” said Bharath Kannan PhD ’22, co-lead author of the research paper.

Challenges in large-scale quantum

One challenge in building a large-scale quantum computer is that an effective way must be found to interconnect quantum information nodes. Conventional techniques are used for standard computers, so those techniques do not translate directly to quantum devices.

Further, large-scale quantum computing requires resilient and extensible hardware to ensure information is transmitted and received.

Quantum network links also process nodes using photons that travel through interconnections called waveguides, which can be unidirectional and move a photon only to the left or right, but it can also be bidirectional.

According to MIT, more existing architectures use unidirectional waveguides, but since each waveguide only moves photons in one direction, more waveguides become necessary when the quantum network expands, making the approach difficult to scale.

“We can get rid of these lossy components if we have a waveguide that can support propagation in both the left and right directions, and a means to choose the direction at will,” says Kannan. “This ‘directional transmission’ is what we demonstrated, and it is the first step toward bidirectional communication with much higher fidelities.”

Next steps for researchers

Having found a technique that achieved more than 96% fidelity, the researchers want to connect multiple modules and use the process to emit and absorb photons. According to MIT, this would be a “major step” in developing a modular architecture that combines many smaller-scale processors into one large-scale, more powerful quantum processor.

“We have just one physical connection that can have any number of modules along the way. This is what makes it scalable. Having demonstrated directional photon emission from one module, we are now working on capturing that photon downstream at a second module,” said co-lead author Aziza Almanakly, an electrical engineering and computer science graduate student in the Engineering Quantum Systems group of the Research Laboratory of Electronics (RLE) at MIT.