Quantum chip circuitry demonstrated

PORTLAND, Ore. — Yale University researchers have demonstrated how to build a quantum computer operating on quantum bits, or qubits, which hold a superposition of quantum states. The computer uses a superconducting "Cooper box" to store oscillating microwave photons which can be read and written without disturbing their quantum states.

Qubits based on the superposition of quantum states can be used to make integrated circuits. "Heisenberg's Uncertainty principle says you can't measure the velocity and position of a particle, and likewise in QED [quantum electrodynamic] circuits you can't measure the voltage and the current at the same time," explained Yale University professor Steven Girvin.

Quantum computers derive their power from enabling a superposition of quantum states to simultaneously perform many parallel operations. Those operations allow quantum computers to perform tasks like breaking encryption codes that are impossible for digital computers. Many quantum-state mechanisms have been demonstrated in physics labs, some of which could serve as building blocks for future quantum computers.

Likewise, Yale's "qutons," or "qubit on a photon," invention may enable quantum computers to be placed on chips even sooner.

The advantages of Yale's method include the relatively small size of its qubit repositories — about a square micron — and the ability to read a qubit's state without disturbing it — the bane of quantum computers to date.

The Yale approach stored qubits in a Cooper-box with over 1 billion superconducting aluminum atoms acting together, thereby providing a kind of quantum momentum that allowed a "probing" photon to read out a qubit's state from the Cooper-box without changing its state.

The researchers predict that their cookbook for quantum computing circuitry using quantum electrodynamics could spawn a range of lab experiments. Soon, the researchers predicted, experiments will test quantum circuitry for a new breed of quantum ICs using optics and photons that interface on-chip with traditional electronic circuits.