150,000 qubits created on a silicon chip: the first optical detection of a single spin appears in Nature

Quantum computers can theoretically solve problems that classical computers cannot solve for billions of years, but only if they have enough qubits. Recently, researchers from Simon Fraser University created more than 150,000 silicon-based qubits on a single chip. They are expected to be connected with light, thus helping to create powerful quantum computers connected to the quantum Internet. .

The related paper "Optical Observation of Single Spins in Silicon" has been published in the latest issue of "Nature" magazine.

##Paper address: https://www.nature.com/articles/s41586-022-04821-y

One of Nature’s Best Natural Qubits: Silicon Spin

We know that classical computers represent data as 1 or 0 by turning transistors on or off. In contrast, quantum computers use qubits. And, due to the surreal nature of quantum physics, qubits can exist in superposition states, in which they essentially represent 1 and 0 simultaneously. This phenomenon allows each qubit to perform two calculations simultaneously. In a quantum computer, the more qubits are connected or entangled, the more computing power increases exponentially.

Currently, quantum computers are noisy intermediate-scale quantum (NISQ) platforms, which means that the number of qubits on them can reach up to several hundred. But to prove useful for practical applications, future quantum computers may need thousands of qubits to help cancel out errors.

Meanwhile, many different types of qubits are being developed, such as superconducting circuits, electromagnetic trapped ions, and frozen neon. In this study, researchers found that spin qubits made of silicon may have good development prospects in the field of quantum computing.

One of the co-corresponding authors of the paper, Stephanie Simmons, quantum engineer & associate professor at Simon Fraser University, said, "Silicon spin is one of the best natural qubits in nature."

Stephanie Simmons

The spin in a spin qubit is a The angular momentum of a particle (such as an electron or an atomic nucleus), which enables it to point up or down in a manner similar to a compass needle pointing north or south. Spin qubits can exist in a superposition state that is positioned bidirectionally simultaneously.

Silicon spin qubits are among the most stable qubits ever created. The technology has advanced rapidly in theory, supported by decades of development work by the global semiconductor industry. Until now, scientists have only measured single spins in silicon electrons. This in turn means that the only way to entangle spins is electromagnetically, and this must be done with qubits in very close proximity to each other, which is difficult to scale from an engineering perspective.

Researchers at Simon Fraser University have optically detected a single spin in a silicon qubit for the first time. Simmons believes this kind of optical access to spin qubits could one day use light to entangle qubits with each other on a chip.

The new spin qubits are based on radiation damage centers, defects inside silicon created using ion implantation or high-energy electron radiation. Specifically, they can be called T centers, each consisting of two carbon atoms, one hydrogen atom and one unpaired electron.

Each T center has an unpaired electron spin and a hydrogen nuclear spin, each of which can serve as a qubit. Among them, the electron spin can remain consistent or stable for more than 2 milliseconds, and the hydrogen nuclear spin can remain consistent for 1.1 seconds. The long lifetime of this silicon spin qubit is already competitive.

A single center in silicon

The researchers printed 150,000 dots called "micropucks" on commercial industry-standard insulating silicon integrated photonic chips. Each microdisk varies in width from 0.5 to 2.2 microns, and they all have an average T center.

Under the microscope: an array of thousands of tiny discs

Under the influence of a magnetic field, the spin qubit state of each T center has slightly different energies, and each emits light of different wavelengths. This allows scientists to detect the state of the T-center spin qubit through optical detection.

Integrated and Optically Coupled T-Center

The wavelength emitted by spin qubits is in the near-infrared O band (1260 to 1360 nm). This means spin qubits can connect with other qubits by emitting light, which is often used in telecommunications networks, to work together within quantum processors and help quantum computers cooperate on the quantum internet.

Additionally, "electronic and nuclear spin qubits can be operated together - the nuclear spin as a long-lived memory qubit and the electron spin as an optically coupled communication qubit, and can be used The microwave fields exchange information between them," Simmons said. "No other physical quantum system can directly link high-performance quantum memory with long-distance photons and demonstrate such commercial prospects. Silicon chips are the top platform for modern microelectronics and integrated photonics."

Future Prospects

Interestingly, scientists already knew about the existence of T centers in the 1970s. “I don’t know why we were the first group to start working on T centers as qubits on silicon chips,” Simmons said. "It is possible that researchers believe that spin-light qubits in silicon chips cannot compete with candidates in other materials such as diamond and silicon carbide. This is a mystery to us."

But current research shows new prospects. "We're very excited about the fundamental scalability of these qubits," Simmons said. "It becomes a new member of the international quantum computer race, and we think the future is very bright."

Although the researchers created many qubits in this new study, "these are not yet Connected to a working quantum computer," Simmons added. "Optical access to these spins will make wiring easier than many other methods, but the technology is still young and there is still a lot of work to be done."

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