Modern technology could undergo a revolution thanks to quantum research thanks to more effective computers, communications, and sensors. However, there are still difficulties in realizing these technological objectives, such as how to properly control information in quantum systems.
In a paper published in Nature Physics, a group of researchers from the University of Rochester, including John Nichol, an associate professor of physics, outlines a new method for controlling electron spin in silicon quantum dots tiny, nanoscale semiconductors with remarkable properties as way to manipulate information in a quantum system.
“The results of the study provide a promising new mechanism for coherent control of qubits based on electron spin in semiconductor quantum dots, which could pave the way for the development of a practical silicon-based quantum computer,” Nichol says.
Using quantum dots as qubits
A regular computer consists of billions of transistors, called bits. On the other hand, quantum computers are built using quantum bits, or qubits. Unlike ordinary transistors, which can be either ‘0’ (off) or ‘1’ (on), qubits are governed by the laws of quantum mechanics and can be both ‘0’ and ‘1’ at the same time.
Long viewed as qubits, silicon quantum dots would allow for the manipulation of the transmission of quantum information through the control of the electron spin. Every electron in a quantum dot has intrinsic magnetism, like a tiny bar magnet.
The results of the study provide a promising new mechanism for coherent control of qubits based on electron spin in semiconductor quantum dots, which could pave the way for the development of a practical silicon-based quantum computer.
Professor John Nichol
Because each electron is a negatively charged particle that acts as though it were rapidly spinning, scientists refer to this magnetic moment as a “electron spin” because it is this effective motion that causes magnetism.
Because it has great gate faithfulness and long coherence times, electron spin is a viable choice for transporting, storing, and processing information in quantum computing. Additionally, it can be manufactured using sophisticated semiconductor manufacturing methods.
The amount of time a qubit has before its quantum information is lost as a result of interactions with a noisy environment is known as its coherence time; a lengthy coherence indicates a longer computation time. High gate fidelity denotes that the quantum action being attempted is carried out precisely as desired.
One major challenge in using silicon quantum dots as qubits, however, is controlling electron spin.
Controlling electron spin
Electron spin resonance (ESR), which requires exposing the qubits to fluctuating radiofrequency magnetic fields, is the conventional technique for regulating electron spin. However, this approach has a number of drawbacks, such as the requirement to produce and accurately manage the oscillating magnetic fields in cryogenic settings, where the majority of electron spin qubits are used.
Researchers typically transmit a current through a wire to produce oscillating magnetic fields, but this might disturb cryogenic surroundings since it produces heat.
Nichol and his colleagues outline a new method for controlling electron spin in silicon quantum dots that does not rely on oscillating electromagnetic fields. The technique relies on a phenomenon known as “spin-valley coupling,” which happens when electrons in silicon quantum dots switch between various spin and valley states. The valley state of an electron refers to a separate quality connected to the electron’s spatial profile, whereas the spin state of an electron refers to its magnetic characteristics.
The spin-valley coupling effect is used by the researchers to regulate the spin and valley states, which in turn controls the electron spin.
“This method of coherent control, by spin-valley coupling, allows for universal control over qubits, and can be performed without the need of oscillating magnetic fields, which is a limitation of ESR,” Nichol says. “This allows us a new pathway for using silicon quantum dots to manipulate information in quantum computers.”
