At the Bleeding Edge of Quantum Computing

Computer chip with four superconducting qubits.  Credit: Image Courtesy of Erik Lucero (2011) via BBC.

Caption for the above photograph: This computer chip includes four superconducting qubits that comprise a quantum mechanical version of a computer microprocessor. Quantum computers are expected to be able to solve various problems that are far too difficult to be handled by conventional computers.

BBC is reporting that a meeting this week of the American Physical Society in Dallas has revealed a chip with advanced quantum components.  This chip (above) has us placed, according to Erik Lucero, a graduate student at the University of California, Santa Barbara, "right at the bleeding edge of actually having a quantum processor.”  From the report:

The 6cm-by-6cm chip holds nine quantum devices, among them four "quantum bits" that do the calculations. The team said further scaling up to 10 qubits should be possible this year.

Rather than the ones and zeroes of digital computing, quantum computers deal in what are known as superpositions - states of matter that can be thought of as both one and zero at once.

In a sense, quantum computing's one trick is to perform calculations on all superposition states at once. With one quantum bit, or qubit, the difference is not great, but the effect scales rapidly as the number of qubits rises. ...

The team's key innovation was to find a way to completely disconnect - or "decouple" - interactions between the elements of their quantum circuit.

The delicate quantum states the team creates in their qubits - in this case paired superconducors known as Josephson junctions - must be manipulated, moved, and stored without destroying them.

The problem is how to maintain the delicate quantum state in order to do this:

Britton Plourde, a quantum computing researcher from the University of Syracuse, said that the field has progressed markedly in recent years.

The metric of interest to quantum computing is how long the delicate quantum states can be preserved, and Dr Plourde noted that time had increased a thousand fold since the field's inception.

"The world of superconducting quantum bits didn't even exist 10 years ago, and now they can control [these states] to almost arbitrary precision."

The abstract for the paper is here.