NIST unveils ‘dimmer switch’ for quantum computer

According to NIST, the switch can reliably tune the interaction strength or rate between qubit and the quantum bus from 100MHz to nearly zero. The advance could enable researchers to control the interactions between many circuit elements in an intricate network, something that would be required in a quantum computer of a practical size. NIST says its switch is the first to produce predictable quantum behaviour over time with the controllable exchange of an individual microwave photon between a qubit and a resonant cavity, which acts as a bus. "We have three different elements working together coherently and without losing a lot of energy," said Michael Allman, a graduate of CU-Boulder. Allman performed the experiments with NIST physicist Ray Simmonds, the principal investigator. All three components (qubit, switch and cavity) were made of aluminium in an overlapping pattern on a sapphire chip. The switch is an rf SQUID (superconducting quantum interference device). The circuit is created with a voltage pulse that places one unit of energy – a single microwave photon—in the qubit. By tuning a magnetic field applied to the SQUID, scientists can alter the coupling energy or transfer rate of the single photon between the qubit and cavity.