Synopsis: Squeezed Photons Up-Converted to Higher Frequency

A new experiment uses nonlinear optics to convert a faint source of correlated photons to higher frequency, conserving their “squeezed” quantum state in the process.
Synopsis figure
Roman Schnabel/Albert Einstein Institute, Germany

Nonlinear optics can boost the frequency of incoming light but, typically, only when that light is intense. Now, for the first time, a group has demonstrated the up-conversion of a faint source of photons in a quantum “squeezed” state. In Physical Review Letters, the authors report that the high-frequency output beam largely preserves the initial quantum correlations between photon pairs, making the technique of potential interest to quantum metrology and quantum communication.

Frequency up-conversion has the potential to improve spatial resolution in imaging and photolithography, both of which are limited by the wavelength of light. The most common technique is frequency doubling, in which two photons from the same source combine in a nonlinear crystal to produce a photon with twice the frequency. Quantum states can be up-converted in this way as well, as long as the source is bright. Many quantum applications, however, require less light to avoid scattering effects.

Roman Schnabel from the Albert Einstein Institute, Germany, and his colleagues have succeeded in quantum up-conversion of a faint source, which in this case consisted of squeezed vacuum states. The squeezing, here, refers to the reduced shot noise (or number fluctuations) in a beam of correlated pairs of infrared photons (1550 nanometers). This squeezed beam combines with a pump beam (810 nanometers) in a mirror cavity containing a nonlinear crystal. Thanks to the high intensity of the pump, squeezed and pump photons interact to generate photons whose frequency is the sum of the combination (giving a visible wavelength of 532 nanometers). The researchers verified that the output light was squeezed, although less than the input. This method of up-conversion could benefit quantum information networks that need to transform infrared light in optical fibers into visible wavelengths for storage. – Michael Schirber


More Features »


More Announcements »

Subject Areas

Quantum InformationOptics

Previous Synopsis

Quantum Information

Cyberattack by Breaking and Entering

Read More »

Next Synopsis

Biological Physics

Live Cell Imaging

Read More »

Related Articles

Synopsis: Getting Plasma in a Twist

Synopsis: Getting Plasma in a Twist

Laser vortex beams can exchange their optical angular momentum with a plasma from which they are reflected. Read More »

Synopsis: Starting Fluid for Laser Fusion
Energy Research

Synopsis: Starting Fluid for Laser Fusion

A laser-based fusion experiment demonstrates that liquid fuel capsules could rectify problems encountered with ice-based fuel capsules. Read More »

Synopsis: Graphene’s Elegant Optics Explained

Synopsis: Graphene’s Elegant Optics Explained

Theoretical calculations anchor graphene’s simple optical absorption in its two-dimensional structure instead of its cone-shaped energy bands. Read More »

More Articles