Synopsis: A smoother quantum measurement

A method called quantum smoothing has been experimentally shown to provide a mean-square measurement error that is a factor of 2 smaller than the quantum limit.
Synopsis figure
Illustration: Alan Stonebraker

The precision of any measurement is fundamentally limited by the standard quantum limit. Often there are classical quantities related to the dynamical evolution of a quantum system one would like to measure, a process known as quantum parameter estimation. This kind of estimation is useful in delicate measurements ranging from gravitational wave detection to quantum computation. Recently, Tsang [1] considered the case of quantum estimation for dynamical systems and proposed a method called quantum smoothing that combines past observations with “future” measurements (that is, a signal is inferred from measurements both before and after a chosen point in time).

As reported in Physical Review Letters, Trevor Wheatley at the University of New South Wales in Canberra, Australia, and co-workers in Australia, Japan, and Canada now have experimentally tested these ideas by considering the problem of estimating the phase of a continuous optical field in the presence of classical noise. The authors use optical modulators to prepare a laser beam in a known state with a predetermined noise signature and then apply an adaptive measurement technique to estimate the optical phase. By including data obtained after time t with data collected before t along with Tsang’s theory, the researchers were able to estimate the phase at t with a mean-square error more than a factor of 2 smaller than the standard quantum limit. – David Voss

[1] M. Tsang, Phys. Rev. Lett. 102, 250403 (2009).


Features

More Features »

Announcements

More Announcements »

Subject Areas

Quantum InformationOptics

Previous Synopsis

Next Synopsis

Optics

Quiet cascade

Read More »

Related Articles

Synopsis: Entangled Photon Source Ticks All Boxes
Quantum Physics

Synopsis: Entangled Photon Source Ticks All Boxes

A quantum-dot-based device combines all of the attributes necessary for producing a reliable source of entangled photons for quantum information applications.  Read More »

Viewpoint: A New Angle on Mapping the Refractive Index
Optics

Viewpoint: A New Angle on Mapping the Refractive Index

3D maps of a sample’s refractive index—used in some biomedical tests—can be directly derived from angle-dependent measurements of light scattering from the sample. Read More »

Focus: <i>Video</i>—Juggling Droplets
Optics

Focus: Video—Juggling Droplets

A pair of microscopic liquid droplets suspended by a laser beam can execute a surprisingly stable “juggling” pattern for up to 30 minutes. Read More »

More Articles