Compiled by Photonics Spectra staff
A tiny, tunable superconducting circuit
can place a single microwave photon in two frequencies simultaneously, potentially
leading to the long-sought “optics table on a chip.”
Researchers at the National Institute of Standards and Technology
have developed the chip-scale device, a microwave version of a common optics experiment
in which a beamsplitter sends a photon into either of two possible paths across
a table of lasers, lenses and mirrors.
The experiment also created the first microwave-based bit for
linear optical quantum computing. It was described in the July 3 online edition
of Nature Physics (doi: 10.1038/nphys2035). This type of quantum computer is envisioned
as storing information in either the polarization of single photons or the path
of a light beam. In contrast, a microwave version would store information in a photon’s
frequency.
NIST’s prototype “optics table on a chip” places
a microwave photon in two frequencies at once. Courtesy of D. Schmidt, NIST.
The newly developed circuit combines components that are used
in superconducting quantum computing experiments: a single-photon source, a cavity
that naturally resonates or vibrates at particular frequencies, and a coupling device
called a SQUID (superconducting quantum interference device).
The NIST scientists tuned the SQUID properties to couple two resonant
frequencies of the cavity. Next, they manipulated a photon to make it oscillate
between different superpositions of the two frequencies. The photons switched back
and forth from equal proportions of both frequencies to an uneven 75/25 split. The
experimental setup trapped photons in the cavity instead of sending them across
an optical table.
Although it is already technically feasible to produce quantum
states in chip-scale devices such as superconducting resonators, the scientists
said they can now manipulate them just as they do in traditional optics setups.
They can control how the new circuit couples various quantum states of the resonator
over time.
As such, they can create sequences of interactions to make simple
optical circuits and reproduce traditional optics experiments. For example, they
can make interferometers based on the frequency of a single photon, or produce special
quantum states of light, such as “squeezed” light.