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| The 4.5-micron diamond ring resonator at the heart of the new single-photon device. |
Diamond might be known for its sparkle, but for quantum physicists it has an entirely different kind of appeal. Diamonds containing nitrogen-vacancy (NV) centers — spots where a nitrogen atom sits next to a missing carbon atom in the crystal lattice — can emit single photons on demand, making them highly attractive as light sources for quantum information applications. The challenge has always been extracting those photons efficiently into a usable optical signal. A team of US physicists has now built a compact integrated device that does exactly that.
At the heart of their design is a tiny ring of diamond, just 4.5 micrometers in diameter, that contains NV centers. The ring acts as an optical resonator: light bouncing around inside it builds up in intensity at specific resonant frequencies. When an NV center inside the ring emits a photon, that photon couples into the resonant mode of the ring and is guided out into an adjacent waveguide — a tiny channel that directs the light where it needs to go.
Why Single-Photon Sources Matter
Single photons are the building blocks of many proposed quantum technologies, from quantum key distribution for ultra-secure communications to linear optical quantum computing. To be useful, a single-photon source needs to emit photons reliably, at a well-defined frequency, and with the emitted photons all being identical to one another — a property called indistinguishability. NV centers in diamond tick many of these boxes, which is why so much effort has gone into engineering efficient ways to use them.
Previous approaches to coupling NV-center emission into optical fibers or waveguides often involved awkward external optics or significant photon losses. An integrated on-chip design like this ring resonator is a significant step toward practical, scalable devices.
A Step Toward Diamond-Based Quantum Devices
The work demonstrates that it's possible to integrate diamond photonic components — resonators and waveguides — at the microscale, which opens the door to more complex all-diamond quantum circuits. Diamond's hardness and chemical stability make it an attractive platform for photonic devices that need to operate in demanding environments. Bringing together the exceptional optical properties of NV centers with integrated photonic engineering represents a genuine advance in the field of quantum photonics.
Source: Physics World
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