Tunable diamond strings promise quantum memory solution

May 31, 2018 // By Rich Pell
Tunable diamond strings promise quantum memory solution
Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (Cambridge, MA) and the University of Cambridge (Cambridge, UK) have developed a quantum memory solution that is as simple as tuning a guitar.

Using quantum bits - or qubits - to carry information requires a quantum memory, an atomic-scale device that can store quantum information and convert it into light to transmit across the network. A major challenge to this is the extremely sensitive nature of qubits - even vibrations of nearby atoms can disrupt their ability to remember information.

Up to now, extremely low temperatures have been used to quiet vibrations, but achieving those temperatures for large-scale quantum networks is prohibitively expensive. However, this new research takes a different approach by using engineered diamond strings that can be tuned to quiet a qubit's environment and improve memory from tens to several hundred nanoseconds - enough time to do many operations on a quantum chip.

"Impurities in diamond have emerged as promising nodes for quantum networks," says Marko Loncar, the Tiantsai Lin Professor of Electrical Engineering at SEAS and senior author of the research. "However, they are not perfect. Some kinds of impurities are really good at retaining information but have a hard time communicating, while others are really good communicators but suffer from memory loss. In this work, we took the latter kind, and improved the memory by ten times."

Impurities in diamond - known as silicon-vacancy color centers - are powerful qubits, say the researchers. An electron trapped in the center acts as a memory bit and can emit single photons of red light, which would in turn act as long-distance information carriers of a quantum internet. But with the nearby atoms in the diamond crystal vibrating randomly, the electron in the center quickly forgets any quantum information it is asked to remember.

"Being an electron in a color center is like trying to study at a loud marketplace," says Srujan Meesala, a graduate student at SEAS and co-first author of the paper on the research. "There is all this noise around you. If you want to remember anything, you need


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