Ten thousand entangled modes

Australia National University PhD student Seiji Armstrong has made a quantum leap towards next-generation computing.

Working with a team in Tokyo, Seiji has created the largest cluster of quantum systems ever – a milestone on the way to super-powerful, super-fast quantum computers.

“The more quantum systems you have in the cluster, the more powerful your quantum computer will be,” he says.

“Previously the world record was 14. But in our experiment we went to more than 10,000 at once.”

Each quantum system can encode a quantum ‘bit’ of information, like the binary system that a traditional computer uses, explains Seiji.

The researchers employed a split laser that contained all 10,000 individually addressable quantum wave packets — photons, essentially. Each photon in the system has an entangled partner in the other half of the beam, which makes it theoretically easier to take measurements. This experimental setup allowed the team to more easily entangle large numbers of quantum bits, which is one of the necessary elements of a quantum computer.

Scalability and control of many quantum simultaneous systems have long held back quantum computing, but maybe not for long. The team, made up of researchers from the University of Tokyo and the Australian National University, has shown that a laser light quantum system is scalable — the previous record used captured ions as the matrix of the quantum system.

The authors of the study do, however, admit that the massive scale of the quantum board has made control of the model tricky. Actually making use of such a large light-based quantum computer requires more work. The method currently being proposed for running calculations through this giant quantum computer is based on sequential quantum teleportation, but improved precision is needed. This is the next step for the researchers, who still have some problems to work out before this method becomes the transistor of the quantum computing era.

Nature Photonics – Ultra-large-scale continuous-variable cluster states multiplexed in the time domain

Quantum computers promise ultrafast performance for certain tasks. Experimentally appealing, measurement-based quantum computation requires an entangled resource called a cluster state, with long computations requiring large cluster states. Previously, the largest cluster state consisted of eight photonic qubits or light modes, and the largest multipartite entangled state of any sort involved 14 trapped ions. These implementations involve quantum entities separated in space and, in general, each experimental apparatus is used only once. Here, we circumvent this inherent inefficiency by multiplexing light modes in the time domain. We deterministically generate and fully characterize a continuous-variable cluster state containing more than 10,000 entangled modes. This is, by three orders of magnitude, the largest entangled state created to date. The entangled modes are individually addressable wave packets of light in two beams. Furthermore, we present an efficient scheme for measurement-based quantum computation on this cluster state based on sequential applications of quantum teleportation.

Arxiv – Optical Generation of Ultra-Large-Scale Continuous-Variable Cluster States

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