Researchers at the Paul Scherrer PSI Institute presented a detailed plan of how faster and better defined quantum bits – qubits – can be created. The central elements are magnetic atoms in the class of so-called rare earth metals, which would be selectively implanted in the crystalline structure of a material. Each of these atoms represents a qubit. The researchers demonstrated how these qubits can be activated, tangled, used as bits of memory and read. They have already published their design concept and support calculations in the magazine PRX Quantum.
On the way to quantum computers, an initial requirement is to create so-called quantum bits or “qubits”: bits of memory that can, unlike classic bits, take on not only the binary values of zero and one, but also any arbitrary combination of those states. “With this, an entirely new type of computing and data processing becomes possible, which for specific applications means an enormous acceleration of computing power”, explains PSI researcher Manuel Grimm, first author of a new article on the qubits theme.
Manuel Grimm is a theoretical physicist at the Paul Scherrer Institute and works on the foundations for the construction of future quantum computers. Credit: Paul Scherrer Institute / Markus Fischer
The authors describe how logical bits and basic computer operations on them can be performed on a magnetic solid: the qubits would reside in individual atoms of the class of rare earth elements, built on the crystalline structure of a host material. Based on quantum physics, the authors calculate that the nuclear spin of rare earth atoms would be suitable for use as an information carrier, that is, a qubit. They also propose that targeted laser pulses can momentarily transfer information to the atomand, therefore, they activate the qubits, through which their information becomes visible to the surrounding atoms. Two of these activated qubits communicate with each other and therefore can be “entangled”. Entanglement is a special property of multiple particle or qubits quantum systems that is essential for quantum computers: the result of measuring one qubit depends directly on the results of measuring other qubits and vice versa.
Faster means less error prone
The researchers demonstrate how these qubits can be used to produce logic gates, most notably the “NOT controlled gate” (CNOT port). Logic gates are the basic building blocks that classic computers also use to perform calculations. If a sufficient number of CNOT ports, as well as ports of a qubit, are combined, all conceivable computational operations become possible. Thus, they form the basis of quantum computers.
This article is not the first to propose quantum-based logic gates. “Our method of activating and entangling qubits, however, has a decisive advantage over previous comparable proposals: it is at least ten times faster,” says Grimm. The advantage, however, is not just the speed at which a quantum computer based on this concept could calculate; above all, it deals with the system’s susceptibility to errors. “Qubits are not very stable. If the entanglement processes are too slow, there is a greater likelihood that some of the qubits will lose their information in the meantime, ”explains Grimm. Ultimately, what the PSI researchers found is a way to make this type of quantum computer not only at least ten times faster than comparable systems, but also less error prone for the same factor.
Reference: “Universal quantum computing using electronuclear wave functions of rare earth ions” by Manuel Grimm, Adrian Beckert, Gabriel Aeppli and Markus Müller, January 21, 2021, PRX Quantum.
DOI: 10.1103 / PRXQuantum.2.010312