Developed by Rochester scientists, the method overcomes the limitations of electron spin resonance.
Quantum science has the potential to revolutionize modern technology with more efficient computing, communication and sensing devices. However, challenges remain in achieving these technological goals, such as how to manipulate information precisely in quantum systems.
In a paper published in natural physics, a group of University of Rochester researchers including John Nicol, an associate professor of physics, outlines a new way to control the electron spin in silicon quantum dots, tiny nanoscale semiconductors with surprising properties. quantum system.
“The results of this work provide a promising new mechanism for coherent control of qubits based on the electron spin of semiconductor quantum dots and may pave the way for the development of practical silicon-based quantum computers.” says Nichol.
Using quantum dots as qubits
A typical computer is made up of billions of transistors called bits. Quantum computers, on the other hand, are based on qubits, also known as qubits. Unlike ordinary transistors that can be either ‘0’ (off) or ‘1’ (on), qubits are controlled by the laws of quantum mechanics and can be both ‘0’ and ‘1’ at the same time. can.
Scientists have long considered using silicon quantum dots as qubits. Controlling the spin of electrons in quantum dots offers a way to manipulate the transfer of quantum information. Every electron in a quantum dot has an intrinsic magnetism, like a tiny bar magnet. Scientists call this “electron spin” (the magnetic moment associated with each electron). This is because each electron is a negatively charged particle that behaves as if it is spinning rapidly and it is this effective motion that generates magnetism.
Electronic spins are promising candidates for information transfer, storage and processing in quantum computing because they offer long coherence times and high gate fidelity and are compatible with advanced semiconductor fabrication techniques. A qubit’s coherence time is the time before quantum information is lost due to interaction with a noisy environment. Longer coherence means longer computation times. High gate fidelity means that the quantum operations researchers are trying to perform are exactly what they want.
However, one of the major challenges in using silicon quantum dots as qubits is controlling the electron spin.
control of electron spin
A standard method to control electron spin is electron spin resonance (ESR). This involves applying an oscillating high-frequency magnetic field to the qubit. However, this method has some limitations, such as the need to generate and precisely control an oscillating magnetic field in the cryogenic environment where most electron spin qubits operate. To generate an oscillating magnetic field, researchers typically pass an electric current through a wire. This can generate heat and disturb the cryogenic environment.
Nichol and his colleagues outline a new method to control electron spin in silicon quantum dots that is independent of oscillating electromagnetic fields. The method is based on a phenomenon called ‘spin-valley coupling’ that occurs when electrons in silicon quantum dots transition between different spin and valley states. The spin state of an electron refers to its magnetic properties, whereas the valley state refers to another property related to the electron’s spatial profile.
The research team applies a voltage pulse to exploit the spin-valley coupling effect and manipulate the spin and valley states to control the electron spin.
“This method of coherent control by spin-valley coupling allows universal control of qubits and can be done without the need for an oscillating magnetic field, which is a limitation of ESR,” says Nichol. “This opens up new avenues for manipulating information in quantum computers using silicon quantum dots.”
Rochester’s work demonstrates how to use the quantum properties of light to transmit information. This is an important step on the road to next-generation computing and communication systems.