Immunizing quantum computers against errors

Building a quantum computer requires reckoning with errors—in more than one sense. Quantum bits, or "qubits," which can take on the logical values zero and one simultaneously, and thus carry out calculations faster, are extremely susceptible to perturbations. A possible remedy for this is quantum error correction, which means that each qubit is represented redundantly in several copies, such that errors can be detected and eventually corrected without disturbing the fragile quantum state of the qubit itself. Technically, this is very demanding. However, several years ago, an alternative proposal suggested storing information not in several redundant qubits, but rather in the many oscillatory states of a single quantum harmonic oscillator. The research group of Jonathan Home, professor at the Institute for Quantum Electronics at ETH Zurich, has now realised such a qubit encoded in an oscillator. Their results have been published in the scientific journal Nature.