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08 Jul 2010
An ion trap containing a built-in optical fibre could benefit quantum computing applications.
Physicists at the US National Institute of Standards and Technology (NIST) have created an ion trap with a built-in optical fibre that collects light emitted by single ions, allowing quantum information stored in the ions to be measured. The advance could simplify quantum computer design and serve as a step toward swapping information between matter and light in future quantum networks (Phys. Rev. Lett. 105 023001).
The NIST device uses a 1 mm2 ion trap. The new trap design is intended as a prototype for eventually pairing single ions with single photons, to make an interface enabling matter qubits to swap information with photon qubits in a quantum computing and communications network.
The researchers use ions as qubits to store information in experimental quantum computing, which may some day solve certain problems that are intractable today. An ion can be adjustably positioned 80–100 µm from an optical fibre, which detects the ion's fluorescence signals indicating the qubit's information content.
"The design is helpful because of the tight coupling between the ion and the fibre, and also because it's small, so you can get a lot of fibres on a chip," explained NIST postdoctoral researcher Aaron VanDevender.
The team used magnesium ions to show the potential of its new device. Light emitted by an ion passes through a hole in an electrode and is collected in the fibre below the electrode surface (see image). By contrast, conventional ion traps use large external lenses typically located 5 cm away from the ions – about 500 times farther than the fibre – to collect the fluorescence.
The fibre method currently captures less light than the lens system but is adequate for detecting quantum information because the ions are extremely bright, producing millions of photons per second, VanDevender says.
Optical fibres may handle large numbers of ions more easily than the bulky optical systems, because multiple fibres may eventually be attached to a single ion trap. The authors expect to boost efficiency by shaping the fibre tip and using anti-reflection coating on surfaces.
Photons are used as qubits in quantum communications, the most secure method known for ensuring the privacy of a communications channel. In a quantum network, the information encoded in the "spins" of individual ions could be transferred to, for example, electric field orientations of individual photons for transport to other processing regions of the network.
This research was supported by the Defense Advanced Research Projects Agency (DARPA), National Security Agency, Office of Naval Research, Intelligence Advanced Research Projects Activity, and Sandia National Laboratories.
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