Hertz Fellow Mollie Schwartz Improving Microwave Amplification for Use in Quantum Computers

October 20, 2015

Quantum computing holds the promise of someday providing computational speed and power far beyond the silicon-based computers we have today. However, one candidate for such technology, superconducting quantum computers, relies on circuits that behave like an artificial atom, so experimenters will need devices that can detect electrical signals on the order of a single photon.

That’s where Hertz Fellow Mollie Schwartz comes in. She and her colleagues at UC Berkeley’s Quantum Nanoelectronics Lab and MIT’s Lincoln Laboratory have developed a microwave amplification device able to accurately detect these tiny signals while at the same time adding an extremely small amount of extra noise.

The team’s superconducting “travelling-wave” amplifier took more than three years to develop. Schwartz worked on the measurement and characterization of the samples for the device, supporting the work of cohorts Chris Macklin and Kevin O’Brien at Berkeley, and David Hover and Vladimir Bolkhovsky at MIT Lincoln Labs. The team’s paper was published in the October 16 edition of Science.

“Now we’re in the state of scaling up to many qubit (quantum bit) experiments, so the time is right for an amplifier of this kind,” Schwartz said. “We see it as an enabling technology that will be extremely useful.”

Mollie Schwartz-Hertz Fellow

Through a technique called “resonant phase-matching,” the team was able to demonstrate two critical improvements over previous microwave amplifiers, which tend to either be excessively noisy or amplify only over a narrow range of frequencies. The new amplifier increases the bandwidth from tens of MHz to several GHz, and boosts the dynamic range (i.e., the maximum total power that can be effectively amplified) of current technology by nearly two orders of magnitude, enabling simultaneous measurement of up to 20 qubits.

Schwartz, 28, said the device will be a critical tool to developing superconducting quantum systems in the future. Scheduled to finish up her PhD in physics in May 2016, Schwartz is working on her doctoral thesis, which broadly deals with the coupling of qubits to noisy environments.

“I found myself really enjoying taking a problem and finding out what the universal building blocks are,” Schwartz said. “We’re making a lot of progress, but there’s still a lot to be done with the fundamentals of quantum science.”

Schwartz is currently on the job hunt, and is exploring opportunities in academia, private industry and the national laboratories. In her spare time, she enjoys teaching Israeli folk dancing, learning to salsa, and running.