Transferring Quantum Information Across a Quantum Bus

Austrian Researchers Have Designed a Quantum Bus

As you know from reading this blog, quantum computing is as fragile as it is exciting. Quantum systems are extremely sensitive to noise and interference, making computing with them quite challenging. Engineers need to keep many physical implementations of quantum memory isolated and cooled to extremely low temperatures to maintain their integrity. Quantum memory and quantum processor components have different noise thresholds.  That means that different error correction codes are used to protect them against noise, making it harder for them to exchange information. Researchers at the University of Innsbruck have designed a quantum bus to address this communications challenge.

Hendrick Poulsen Nautrup, Hans Briegel, and Nicolai Friis have proposed using a technique called subsystem lattice surgery to create an interface between quantum memory and processors.  The team is now collaborating with experimental physicist Rainer Blatt’s lab (also at the University of Innsbruck). They are working to perform their own proof-of-principle experiment. “In principle, labs across the globe already have all the tools available to perform a proof-of-principle experiment,” Poulsen said in a recent interview. “I can’t tell you too much about it, because it is underway and has not been completed yet, but the intermediate results are sure exciting.”

The First Quantum Bus?

At a high level, the idea is to perform lattice surgery—alter targeted elements of the encoded qubits—to temporarily unite the processor and the memory.  Quantum information can transfer back and forth once the two component are joined together.  This is similar to a bus in a traditional computer architecture.  The University claims this is a step toward a universal quantum computer.  No doubt this will be a valuable asset at some point in the emergence of such a machine.  However, it seems to me there are more basic challenges to overcome first, like keeping qubits stable over time.

You may remember that Professor Schoelkopf’s lab at Yale claims to have developed the first “quantum bus.”  This appears to be another case of people in the field using the same terminology to mean two different things. (Where have you heard that before?) In Schoelkopf’s case, he’s referring to distributing information between two qubits on the same chip.

Still, I will keep an eye on this Austrian project in hopes that it’s a sign of good things to come.  For my part, I hope the University’s assertion is prophetic.