A new study by Princeton University scientists paves the way for the use of silicon-based technologies in quantum computing and will help increase their use as an alternative to other quantum computing technologies, such as superconductors and trapped ions.
During the study, scientists managed to achieve an unprecedented level of accuracy of more than 99.8% using a two-qubit silicon quantum device. To date, this is the highest accuracy for a two-bit gateway in a semiconductor. Accuracy, which consists in the ability of a qubit (the smallest unit of information in a quantum computer) to perform operations without errors, is a key point for practical high-performance quantum computing.
Researchers around the world are trying to figure out which technologies, superconducting qubits, trapped ions or silicon spin qubits, are most suitable for the role of basic elements of quantum computing. And, importantly, experts are studying which technologies are most suitable for commercial use.
With the help of a silicon device, the so-called double quantum dot, Princeton University scientists were able to capture two electrons and make them interact with each other. Thus, they managed to use the spin state of each electron as a qubit, and the interaction between the electrons allowed these qubits to be entangled.
A qubit is a kind of quantum bit, which is the smallest unit of data in computer technology. Like a bit, a qubit is encoded with information that can have a value of zero or one.
However, unlike a bit, a qubit can use the principles of quantum mechanics, which allows it to perform tasks that an ordinary bit cannot do. For example, it can have a superposition of zeros and ones, that is, it can be both zero and one at the same time. Because of this, quantum computers have a huge advantage over conventional ones.
In spin qubits, “spin” means the angular momentum of an electron. This is a quantum property that manifests itself in the form of a tiny magnetic dipole that can be used to encode information. An example is a compass needle pointing to the south and north poles and rotating in accordance with the Earth’s magnetic field.
Spin is a property of an electron used in silicon–based quantum devices. For comparison, conventional computers work by controlling the negative charge of an electron.
In general, silicon spin qubits have advantages over other types of qubits.
“The idea is that each system should scale up to many qubits. Currently, other qubit systems have real physical scalability limitations. Size can be a real problem for these systems. There are not so many places where all this can be squeezed in,” explained Adam Mills, the head of the study.
Silicon spin qubits consist of single electrons and are extremely small. The device used in the course of the study had a diameter of only 100 nm, whereas the diameter of conventional superconducting qubits exceeds 300 microns, so many of them cannot fit on the chip.
Another advantage of silicon spin qubits is that conventional electronics today are based on silicon technology. According to the authors of the study, to create a million or ten million qubits for practical use, only a solid-state system that can be scaled using the standard semiconductor industry is suitable.