New model for better and faster Qubits



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Advanced quantum computer concept

Researchers at the Paul Scherrer Institute PSI have come up with a detailed blueprint for how faster and better defined quantum bits – qubits – can be created. The central elements are magnetic atoms of the class of so-called rare earth metals, which would be selectively implanted in the crystal lattice of a material. Each of these atoms represents a qubit. Researchers have demonstrated how these qubits can be activated, entangled, used as memory bits, and read. They have now published their design concept and supporting calculations in the journal PRX file.

On the way to quantum computers, an initial requirement is to create so-called quantum bits or “qubits”: bits of memory that can, unlike conventional bits, take not only binary values ​​of zero and one, but also any arbitrary combination. of these states. “With this, a whole new kind of computation and data processing becomes possible, which for specific applications means a huge acceleration in computing power”, explains Manuel Grimm, researcher at PSI, first author of a new article on the theme of qubits.

Manuel Grimm

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 in a magnetic solid: qubits would reside on individual atoms of the rare earth element class, embedded in the crystal lattice 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, i.e. a qubit. They further propose that the targeted laser pulses could momentarily transfer the information to the atomelectrons and thus activate qubits, whereby their information becomes visible to surrounding atoms. Two of these activated qubits communicate with each other and can therefore be “entangled”. Entanglement is a special property of quantum particle systems or multiple qubits which is essential for quantum computers: the measurement result of one qubit depends directly on the measurement results of other qubits, and vice versa.

Faster means less error prone

Researchers demonstrate how these qubits can be used to produce logic gates, including the “UNControlled gate” (CNOT gate). Logic gates are the basic building blocks that classic computers also use to perform calculations. If enough such CNOT gates as well as single qubit gates are combined, all imaginable computational operations become possible. They thus form the basis of quantum computers.

This article is not the first to propose quantum 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,” explains 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 vulnerability of the system to errors. “The 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 prone to errors by the same factor.

Reference: “Universal Quantum Computing Using Electronuclear Wavefunctions of Rare-Earth Ions” by Manuel Grimm, Adrian Beckert, Gabriel Aeppli and Markus Müller, January 21, 2021, Like PRX.
DOI: 10.1103 / PRXQuantum.2.010312



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