Synopsis: Noise and the Single Qubit

A strongly driven single-ion qubit offers a method for performing spectrum analysis with high resolution.
Synopsis figure
S. Kotler et al., Phys. Rev. Lett. (2013)

A qubit made of a single trapped ion loses coherence in a noisy environment. Researchers have turned this seeming annoyance into a useful tool: by watching the spin, they can measure how noise sources vary with frequency. So far, single-qubit spectrum analyzers have only been studied for cases in which the external noise barely perturbs the ion. In a paper in Physical Review Letters, Shlomi Kotler and colleagues at the Weizmann Institute of Science, Israel, report a single-qubit device in which the coupling to the noise is strong. They find that these conditions result in significantly better spectral resolution.

Decoherence spectroscopy relies on the fact that a quantum system modulated at a particular frequency is highly sensitive to noise at that frequency. By varying the modulation frequency, the noise spectrum can be mapped out. If the noise source is too strong, however, the method fails. Kotler et al. showed theoretically that spectral analysis under these conditions is still possible if the noise source consists of discrete frequencies. To test the idea, the authors used a single trapped strontium ion to analyze the noisy background magnetic fields generated by power lines in their lab. They were able to detect the frequency peaks in the ambient magnetic noise with resolution about a factor of 10 better than expected in a weak-coupling measurement.

The Weizmann researchers suggest a number of applications for their single-spin analyzer, including measurement of brain waves with magnetoencephalography and detection of fields near nitrogen-vacancy-center qubits in diamond. – David Voss


Announcements

More Announcements »

Subject Areas

Spintronics

Previous Synopsis

Next Synopsis

Related Articles

Viewpoint: X Rays Expose Transient Spins
Magnetism

Viewpoint: X Rays Expose Transient Spins

X-ray magnetic circular dichroism detects the transient magnetic moments that are induced in a nonmagnetic material by spin injection from a ferromagnet. Read More »

Viewpoint: Electrical Signal Picks Up a Magnet’s Heartbeat
Magnetism

Viewpoint: Electrical Signal Picks Up a Magnet’s Heartbeat

Excitations in a magnet coupled to a microwave cavity can be detected electrically, providing a new way to study magnets in the quantum regime. Read More »

Viewpoint: A Boost for Superconducting Logic
Superconductivity

Viewpoint: A Boost for Superconducting Logic

A new choice of materials leads to more practically useful superconducting spin valves. Read More »

More Articles