New silicon-based quantum bits produce photons that may provide the basis for quantum internet

Quantum computing research is the gift that keeps on giving. As teams of physicists, computer scientists and engineers around the world race to produce the first scalable, working quantum computers and quantum internet, different architectures are emerging.

Researchers at Canada’s Simon Fraser University have taken a new look at silicon – an element already at the centre of modern computer chips – to make quantum bits, or “qubits”.

Set to revolutionise computing, quantum machines bring promise of better, faster, more efficient devices which can store multidimensional computing data of much greater complexity than an ordinary bit.

To do this, quantum computers will make use of the strange phenomena associated with the quantum world of particles, atoms and molecules. Instead of just using zeroes and ones to store information, transistors in quantum computers will be able to store zeroes, ones, or a mixture of zero and one, for extra computing power.

All of which is well and good, but how do you make a quantum transistor? Well, there are lots of embryonic machines taking different approaches.

Read more: Australian researchers develop a coherent quantum simulator

One approach, published in Nature, is to use the “photon-spin” produced by defects in silicon as a transistor. Spin is an intrinsic property of particles like photons, which is a type of angular momentum. Particles can be thought of as spinning like a top – the particles are either spinning up or down (like turning the top upside down). Up and down can therefore be translated into ones and zeroes.

Silicon Quantum Technology team of Simon Fraser University. Credit: Photonic.

The team, working out the Silicon Quantum Technology Lab at Simon Fraser University, observed 150,000 of these photon-spin qubits in their experiments. The qubits are some of the most stable and long-lived in the world.

The data revealing the first optical observation of spins in silicon. Two-laser scans of a single spin reveal signature spin-split central peaks; here the experimental data is visualised as a mosaic heatmap. Credit: Photonic.

The researchers produced the photon-spin qubits in “T centres” – defects caused by replacing a silicon atom with two carbon and one hydrogen atom in the matrix of silicon atoms. The defect is, thus, also relatively well guarded from external effects due to its immersion in the silicon matrix. The T centre emits a photon (particle of light).

“This work is the first measurement of single T centres in isolation – and actually, the first measurement of any single spin in silicon to be performed with only optical measurements,” says co-leader of the project Stephanie Simmons, who is Canada Research Chair at Silicon Quantum Technologies.

“An emitter like the T centre that combines high-performance spin qubits and optical photon generation is ideal to make scalable, distributed, quantum computers, because they can handle the processing and the communications together, rather than needing to interface two different quantum technologies, one for processing and one for communications,” Simmons says.

The team believes this can be applied to form a “quantum internet”. T centres have the advantage of emitting at the same wavelength of light used in today’s fibre communications and networking equipment.

An optical microscope image of an array of integrated photonic devices, used to perform the first all-optical single-spin measurement in silicon. Tens of thousands of such ‘micropuck’ devices were fabricated on a single silicon photonic chip. Credit: Photonic.

“With T centres, you can build quantum processors that inherently communicate with other processors,” Simmons explains. “When your silicon qubit can communicate by emitting photons in the same band used in data centres and fibre networks, you get these same benefits for connecting the millions of qubits needed for quantum computing.”

Using silicon in quantum computers is an attractive prospect as the global semiconductor industry is already able to inexpensively manufacture high-precision silicon computer chips at massive scales.

“By finding a way to create quantum computing processors in silicon, you can take advantage of all of the years of development, knowledge and infrastructure used to manufacture conventional computers, rather than creating a whole new industry for quantum manufacturing,” Simmons adds. “This represents an almost insurmountable competitive advantage in the international race for a quantum computer.”

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