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New Quantum States For Better Quantum Memories


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An artificial diamond under the optical microscope; nitrogen defects make the diamond fluoresce.

A research team is working to develop quantum memories based on nitrogen atoms and microwaves, using synthetic diamonds in which individual nitrogen atoms are implanted.

Credit: Technical University of Wien (Austria)

Researchers at Austria's Technical University of Wien (TU Wien), in collaboration with Japan's NTT, are moving toward new quantum memory concepts using nitrogen atoms and microwaves.

Project leader Johannes Majer says the atoms are implanted within synthetic diamonds, and the coupling of microwaves to the atoms' quantum state supports "a quantum system in which we store and read information." However, the inhomogeneous lengthening of the microwave transition in the diamond's nitrogen atoms means the quantum state can no longer be reliably read out after approximately half a microsecond.

Majer's team used "spectral hole burning," which enables data to be stored in the optical range of inhomogeneously broadened media, and refined it for supra-conducting quantum circuits and spin quantum memories.

"The transitions areas in the nitrogen atoms have slightly different energy levels because of the local properties of the not-quite-perfect diamond crystal," says former TU Wien researcher Stefan Putz. "If you use microwaves to selectively change a few nitrogen atoms that have very specific energies, you can create a 'Spectral Hole.' The remaining nitrogen atoms can then be brought into a new quantum state, a...'dark state,' in the center of these holes."

The researchers note this technique extends the quantum states' lifetime to about five microseconds.

From Technical University of Wien (Austria)
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