The study investigates coherent manipulation of electron spin in silicon

The study investigates coherent manipulation of electron spin in silicon

Electrons in silicon experience coupling between their spin (up and down arrows) and valley states (blue and red orbitals). In the presence of a DC voltage (blue glow) the electron can undergo coherent spin-valley oscillation. Image credit: Mike Osadcio.

In recent years, many physicists and computer scientists have been working on quantum computing technologies. These technologies are based on qubits, which are the basic units of quantum information.

Unlike classical bits, which have a value of 0 or 1, qubits can exist in them superposition cases, so their value can be 0 and 1 at the same time. Qubits can be made from different physical systems, incl electronsAnd nuclear spins (eg, the spin state of the nucleus), photons, and superconducting circuits.

Confined electron spins silicon Quantum dots (that is, small silicon-based structures) have shown particular promise as qubits, particularly because of their long coherence times, high gate resolution, and compatibility with existing semiconductor fabrication methods. Multiple control coherently electron spin statesHowever, it can be a challenge.

Researchers at the University of Rochester recently presented a new strategy for coherently dealing with single or multiple electron spins in silicon quantum dots. This method was presented in a research published in nature physicsit could open up new possibilities for developing reliable, high-performance quantum computers.

“As with many scientific experiments, we were initially investigating an unrelated topic, when we started noticing all sorts of coherent oscillations that appeared in our data.” John Nichol, one of the researchers who conducted the study, told “It took us a while to come up with the theoretical explanation, but once we did, everything fell into place. Spin-valley coupling has been explored before many times, but coherent transitions between different spin states have not been directly mediated.”

The electron spin control strategy in silicon proposed by Nicol et al. takes advantage of spin-valley coupling, which is the interaction between electron spin and valley states. Electrons in silicon quantum dots have spin and valley quantum numbers. The spin state can be “up” or “down”, while the valley state can be + or -.

“In particular magnetic field“For example, the energy of the higher, + state can be approximately equal to the energy of the lower, – state,” Nicol explained. Since the energy difference between the + and – states depends on the electric fields, we can use a voltage pulse to bring in, + exactly with the resonance down, -. When this happens, the electron that was initially prepared in the +-up state will coherently oscillate to the downward, -, back and forth. These are oscillations in the valley of rotation.

To date, the standard method for manipulating electron spins in silicon quantum dots entails the use of time-varying magnetic fields. Nicoll and colleagues show that their strategy enables coherent manipulation of the electron’s spin without the need to use oscillating electromagnetic fields.

“It can be particularly difficult to generate oscillating magnetic fields in refrigerated temperaturesThe spindle-valley coupling eliminates this need, Nicol said. “Another realization is that the valley degree of freedom in silicon is often seen as a ‘flaw’ rather than a feature of silicon qubits, but our work shows that it can be a very useful feature.”

Recent work by this team of researchers highlights the promise of using spin-valley coupling to achieve coherent qubit control based on The electron spins confined to silicon quantum dots. In their next papers, they hope to gain a better understanding of the growth, fabrication, and tuning properties of quantum dots that can influence spin-valley coupling, as this can lead to more information for the fabrication of electron-based quantum computing technologies.

We would also like to explore how one might multi-implementqubit Added Nicol, “One of the challenges is that the magnetic field needs to be tuned separately for each qubit, and we’re looking at realistic ways to do that.”

more information:
Xinxin Cai et al, Spin-valley coherent vibrations in silicon, nature physics (2023). DOI: 10.1038/s41567-022-01870-y

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