New method for controlling electron spin paves way for efficient quantum computers

Quantum science has the potential to revolutionize modern technology with more efficient computers, communication devices and sensors. However, there are still challenges in achieving these technological goals, including how to precisely manipulate information in quantum systems.

In a piece of paper published year Natural Physicsa team of researchers from the University of Rochester, including John Nichol, an associate professor of physics, outlines a new method for controlling electronic spin in silicone quantum dot—microscopic, nanoscale semiconductors with remarkable properties—as a way to manipulate information in a quantum system.

“The results of the study provide a promising new mechanism for tightly controlling electron spin-based qubits in semiconductor quantum dotcould pave the way for the development of a practical silicon-based quantum computer,” said Nichol.

Using quantum dots as qubits

A typical computer consists of billions of transistors, called bits. Quantum computers, on the other hand, are based on quantum bits, also known as qubits. Unlike conventional transistors, which can be “0” (off) or “1” (on), qubits are governed by the laws of quantum mechanics and can be “0” and “1” simultaneous.

Scientists have long considered using silicon quantum dots as qubits; Controlling the spin of electrons in quantum dots would offer a way to control the transmission of quantum information. Each electron in the quantum dot is intrinsically magnetic, like a small bar magnet. Scientists call this an “electron spin”—the magnetic moment bound to each electron—because each electron is a negatively charged particle that behaves as if it were spinning rapidly, and it is this efficient motion that creates magnetism.

Electron spin is a promising candidate for information transmission, storage, and processing in quantum computing because it offers long coherence times and high gate reliability, and is compatible with production techniques. advanced semiconductor manufacturing. Combined time of a qubit is the time before quantum information is lost due to interaction with the noisy environment; Long coherence means longer time to perform calculations. High gate fidelity means that the quantum operation the researchers are trying to accomplish is done exactly as they want it to.

However, a major challenge in using silicon quantum dots as qubits is controlling the electron’s spin.

Electronic spin control

The standard method for controlling electron spin is electron spin resonance (ESR), which involves applying an oscillating radio-frequency magnetic field to qubits. However, this method has several limitations, including the need to precisely generate and control oscillating magnetic fields in cryogenic environments where most electron spin qubits are operated. Normally, to create an oscillating magnetic field, researchers pass an electric current through a wire, and this generates heat, which can disturb the frozen medium.

Nichol and his colleagues outline a new way to control the spin of electrons in silicon quantum dots without relying on oscillating electromagnetic fields. The method is based on a phenomenon called “spin valley coupling”, which occurs when electrons in silicon quantum dots transition between different spin and valley states. While the spin state of an electron refers to its magnetic property, the valley state refers to another property related to the electron’s spatial configuration.

The researchers apply a voltage pulse to exploit the spin-valley coupling effect and manipulate the spin and valley states, which control the spin of the electron.

“This coherent control method, by spin-valley coupling, allows for the universal control of qubits and can be implemented without the need for oscillating magnetic fields, which is a limitation of ESRs,” says Nichol. “. “This gives us a new avenue to use silicon quantum dots to manipulate information in quantum computers.”