» Research » Department of Quantum Science & Technology » Solid state spectroscopy group » Quantum computing
Quantum computers promise the ability to solve certain problems much faster than classical computers. To do this, computing is performed on quantum bits (qubits), which can exist in superposition states in addition to the ordinary binary states 0 and 1. The challenge of quantum computing is that these superposition states are easily destroyed by interactions with the environment.
This means that quantum computing requires a system with weak interactions between the qubits and the environment, but also strong interactions amongst the qubits to enable computing to be performed. The first requirement means a long coherence time is needed, something rare earth ions in solids are well known for. The second requirement can be satisfied by making qubits out of neighbouring rare earth ions in the crystal, since these have separations of a few Angstroms, and so can have extremely strong interactions, >10 MHz.
We are investigating using fully concentrated rare earth crystals to develop ensemble-based, frequency addressed quantum computers. The ensemble is made up of pseudo-molecules embedded the crystal, created by doping the crystal at low concentration. Hyperfine states, with their long coherence times, are used for the qubit states and each qubit in the pseudo-molecule has a unique optical frequency, allowing the qubit states to be manipulated and initialised with a laser. This ensemble approach means that readout is straightforward, while the strong interactions between neighbouring ions ensure high-fidelity quantum computing gates.
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