“Generating remote entanglement is a crucial step toward building a large-scale quantum processor from smaller-scale modules,” according to MIT graduate student Beatriz Yankelevich. This is a reflection of the revolutionary effect of a new quantum interconnect device developed by scientists at the Massachusetts Institute of Technology. The device allows direct communication between quantum processors, one of the largest scaling challenges in quantum computing systems.
The heart of this innovation is a superconducting waveguide, a high-tech wire that can transmit microwave photons—carriers of quantum information between processors. In contrast to traditional “point-to-point” designs, in which information travels sequentially through nodes and which tend to accumulate error rates, MIT’s device allows for “all-to-all” communication. This is the first ability of every processor within a quantum network to talk directly to any other and with no middleman and with much better efficiency and scalability.
The researchers showed the processor’s ability with a two-node quantum processor network, each four qubits. Qubits, four simple units of quantum computing, were assigned to the ones that emitted and absorbed photons and to the ones that were able to store information. With precisely tuned microwave pulses, the researchers excited a qubit to create a photon and guided it down the waveguide to a receiver processor. Fine control permitted the demonstration of remote entanglement to become possible, a phenomenon in which two processors become correlated even though they are located a distance from each other.
Entanglement is crucial for quantum computing as it allows processors to behave as if they are adjacent to each other, independent of location. Obtaining remote entanglement, however, is not that easy. The photon needs to be absorbed maximally by the receiving processor, complicated by imperfections in the waveguide, like wire joints and wiring that bend the photon during its path. “The challenge in this work was shaping the photon appropriately so we could maximize the absorption efficiency,” says study lead author Aziza Almanakly.
To get around this obstacle, the team utilized reinforcement learning, a type of artificial intelligence, to maximize the shape of the photon prior to transmission. The algorithm shaped the protocol pulses to pre-distort the photon such that its absorption rate was sped up by several orders of magnitude. It achieved an over 60% absorption efficiency, a benchmark that established the entangled state fidelity and represented a significant quantum network milestone.
The implications of this accomplishment go far beyond the first demonstration. “”We can use this architecture to create a network with all-to-all connectivity. This means we can have multiple modules, all along the same bus, and we can create remote entanglement among any pair of our choosing,” Yankelevich goes on to say. The system’s modularity enables researchers to connect several quantum modules to one waveguide, enabling effortless photon transfer and the building of larger distributed quantum networks.
On the horizon, the team anticipates further optimization to improve performance. Future advancements may involve building components in three dimensions to shrink distances photons have to travel or accelerating the protocol to limit error buildup. “In principle, our remote entanglement generation protocol can also be expanded to other kinds of quantum computers and bigger quantum internet systems,” Almanakly says.
This achievement is one of the landmarks in the road to functional large scale quantum computing. By crossing the gap from experimental advancements toward scalable uses, MIT’s interconnect device both pushes the innovation of quantum computing and opens doors to new paradigmatic computation at large. It is as simple as the words of the lead author of this paper, William D. Oliver, to characterize the achievement when he says that, “We are enabling ‘quantum interconnects’ between distant processors, paving the way for a future of interconnected quantum systems.”
The research, which was published in Nature Physics, is a testament to the collaborative work of MIT scientists and their peers, funded by the U.S. Army Research Office, the AWS Center for Quantum Computing, and the U.S. Air Force Office of Scientific Research. With the future of quantum computing unfolding, breakthroughs such as this interconnect device will be central to defining the future of technology and computation.
