Past Winner
2004 NSERC Doctoral Prize

Alexandre Blais

Physics

Université de Sherbrooke

A Canadian physicist has gained national and international attention for helping pave the way to the creation of the world's first quantum computer, and doing the work while a graduate student.

Though Dr. Alexandre Blais calls it a "small step" on a long journey, his research findings improve the practical aspects of quantum bit, or qubit, construction, and offer a new way of maintaining quantum coherence, the key to a successful quantum processor.

"If qubits are to be useful in any way, it should be possible for us to control them and read out their value," says Dr. Blais, a recent Université de Sherbrooke Ph.D. recipient, and winner of a 2004 NSERC Doctoral Prize – one of Canada's premier awards for new doctoral graduates.

"This means that qubits can't be too small and isolated from everything else. This is a huge contradiction because things that aren't very small and aren't well isolated from their surroundings usually don't behave quantum mechanically, rather their behaviour is explained by the laws of classical, Newtonian physics."

To circumvent the loss of quantum mechanical properties (called decoherence), Dr. Blais turned to another realm of high-interest physics research: superconductors. These materials have the advantage that under certain conditions, usually at very low temperatures just above absolute zero Kelvin (-273°C), all of their electrons behave as if they were one – a condition called a Bose-Einstein condensate.

Dr. Blais, in collaboration with Dr. Alexandre Zagofkin of Vancouver's D-Wave Systems, proposed the creation of one of the first types of superconductor-based qubits. The design was based on a millionth-of-a-metre-sized junction (large by quantum mechanical standards) between two high-temperature aluminium superconductors. This approach is now being explored around the world by at least three different teams of experimenters.

"A practical advantage is that there is already a lot of expertise in the fabrication of superconducting electrical circuits," says Dr. Blais, now a postdoctoral fellow in the Yale University lab of condensed-matter physicist Dr. Steve Girvin.

Building on the qubit construction problem tackled early in his doctoral work, Dr. Blais turned to the more vexing issue of quantum entanglement, or maintaining coherence with a group of qubits. The research involved Dr. Zagofkin, and Dr. Blais' Université de Sherbrooke Ph.D. advisors Drs. André-Marie Tremblay and Serge Lacelle.

In order to perform a logical operation, two bits, or qubits, must communicate. For example, in an existing semiconductor computer, one bit might be "0" and the other "1," and this combination results in a specific operation. However, with a quantum computer, if the qubits interact with one another directly, they entangle and lose their individual characteristics.

"Entanglement is one of the strangest predictions of quantum mechanics, but it turns out to be what makes a quantum computer powerful. What I suggested is a way to generate entanglement in a controllable way," says Dr. Blais.

He proposed a unique system in which a third, easy-to-build qubit is used as a communication go-between.

"The two qubits never talk to one another directly, they only talk to a third system which is the mediator of entanglement," he says.

Dr. Blais has filed a patent on the process, and in 2003, a group led by the University of Maryland's Dr. Chris Lobb reported in Science that they'd been able to successfully build a simplified version of this qubit system.

At Yale, Dr. Blais is extending his journey into the realm of quantum weirdness by applying his expertise with superconducting materials to cavity quantum electrodynamics. He's part of a research group that's using micron-sized pieces of superconducting aluminium, placed in a tiny cavity, to study the interaction between the equivalent of a single atom (the aluminium) and a single photon.

Under these conditions the aluminium circuit even interacts with "zero photons," says Dr. Blais with a quantum chuckle. "It's very interesting physics."