Entangled photon pairs are generated by and propagate away from qubits, which are arranged along a waveguide. Photo credit: Sampson Wilcox
The new technology offers a way to connect between processors and opens the way to a complete one Quantum computing Platform.
WITH Researchers using superconducting quantum bits attached to a microwave transmission line have shown how the qubits can, when needed, generate the photons, or particles of light, necessary for communication between quantum processors.
Progress is an important step in achieving the connections that would allow a modular quantum computing system to perform operations at rates that are exponentially faster than traditional computers can.
“Modular quantum computing is a technique to achieve large-scale quantum computation by dividing the workload across multiple processing nodes,” said Bharath Kannan, MIT graduate and lead author of an October 7, 2020 article on the subject Advances in science. “However, these nodes are generally not in the same place, so we need to be able to communicate quantum information between distant locations.”
In classic computers, wires are used to pass information back and forth through a processor during computation. In a quantum computer, the information itself is quantum mechanical and fragile and requires new strategies to process and communicate information at the same time.
“Superconducting qubits are a leading technology these days, but generally only support local interactions (closest neighbor or qubits very close). The question is, how do you connect to qubits in remote locations, ”said William Oliver, Associate Professor of Electrical and Computer Science, MIT Lincoln Laboratory Fellow, Director of the Center for Quantum Engineering and Associate Director of the Research Laboratory of Electronics. “We need quantum connections that are ideally based on microwave waveguides and that can carry quantum information from one place to another.”
This communication can be over the microwave transmission line or the waveguide, as the stimuli stored in the qubits create pairs of photons that are emitted into the waveguide and then travel to two distant processing nodes. The identical photons are said to be “entangled” and act as a system. If they travel to remote processing nodes, they can distribute this entanglement in a quantum network.
“If necessary, we generate the entangled photons with the help of the qubits and then transfer the entangled state to the waveguide with very high efficiency, essentially unity,” says Oliver.
The research reported in the Advances in science Paper uses a relatively simple technique, says Kannan.
“Our work presents a new architecture for generating photons that are spatially entangled in a very simple way, using just a waveguide and a few qubits that act as photonic emitters,” says Kannan. “The entanglement between the photons can then be transmitted into the processors for use in quantum communication or interconnection protocols.”
While the researchers said they had not yet implemented these communication protocols, their ongoing research is in this direction.
“In this thesis, we have not yet carried out communication between processors, but have shown how we can generate photons that are useful for quantum communication and connection,” says Kannan.
Previous work by Kannan, Oliver, and colleagues introduced a waveguide quantum electrodynamics architecture with superconducting qubits, which are essentially some kind of artificial giant atom. This research has shown how such an architecture can perform low-error quantum computation and exchange quantum information between processors. This is achieved by adjusting the frequency of the qubits to adjust the qubit-waveguide interaction strength so that the fragile qubits can be protected from waveguide-induced decoherence to perform qubit operations with high fidelity, and then readjusting the qubit frequency so that the qubits can give their quantum information in the form of photons to the waveguide.
In this article, the ability of waveguide quantum electrodynamics to generate photons was presented and it was shown that the qubits can be used as quantum emitters for the waveguide. The researchers showed that quantum interference between the photons emitted into the waveguide creates entangled, wandering photons that move in opposite directions and can be used for long-distance communication between quantum processors.
The generation of spatially entangled photons in optical systems is typically achieved using spontaneous parametric downconversion and photodetectors, but the entanglement created in this way is generally random and therefore less useful in enabling the on-demand communication of quantum information in a distributed system.
“Modularity is a key concept for any expandable system,” says Oliver. “Our goal is to demonstrate the elements of quantum compounds that should be useful in future quantum processors.”
Reference: “Generation of spatially entangled wandering photons with waveguide quantum electrodynamics” by B. Kannan, DL Campbell, F. Vasconcelos, R. Winik, DK Kim, M. Kjaergaard, P. Krantz, A. Melville, BM Niedzielski, JL Yoder, TP Orlando , S. Gustavsson and WD Oliver, October 7, 2020, Advances in science.
DOI: 10.1126 / sciadv.abb8780
