Researchers Make History by Gaining Complete Control of the Quantum Dot Qubit System

For the development of dependable and extremely powerful quantum computers, the ability to precisely control interacting spins in quantum systems is crucial.

This has shown to be especially difficult for quantum-dot-based nanoscale systems with multiple spins (i.e., small semiconductor devices).

A quantum dot-based device with four singlet-triplet qubits was recently shown to be universally controllable by researchers at Delft University of Technology (TU Delft). Their work, which was reported in Nature Nanotechnology, may pave the way for the effective expansion of quantum information processing systems.

According to Lieven Vandersypen, the paper's senior author, when they first loaded a 4x2 quantum dot array with one spin per dot, they were attempting to adjust and calibrate the exchange contact between all of the nearby spins, as reported by Physics.org. Eventually, they discovered that they had successfully accomplished universal control of four so-called singlet-triplet qubits (joint states of two spins) via time domain measurements. They then worked very hard to establish entanglement throughout the qubit array and to meticulously benchmark the quantum processes.

Prior to this discovery, systems with up to two interacting singlet-triplet qubits could be universally controlled by quantum physicists and engineers. As a result, Vandersypen and his associates became the first to master a bigger system of four singlet-triplet qubits based on quantum dots.

According to Vandersypen, baseband voltage pulses may be used to drive single-qubit processes, and each qubit in their system has two spins. These switch between two distinct values, which correspond to two distinct qubit rotation axes, in the spin-spin exchange interaction. Gate voltage pulses are also used to initiate the exchange coupling between spins of separate qubits in two-qubit gates.