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).


More Announcements »

Subject Areas

Quantum InformationOptics

Previous Synopsis

Next Synopsis


Quiet cascade

Read More »

Related Articles

Synopsis: Valley of the Dichalcogenides
Semiconductor Physics

Synopsis: Valley of the Dichalcogenides

A magnetic field can be used to change the “valley” states that emerge in certain semiconductors. Read More »

Synopsis: Time Optimization in Quantum Computing  
Quantum Information

Synopsis: Time Optimization in Quantum Computing  

New experiments find the fastest way to manipulate logic gates with two qubits as inputs. Read More »

Synopsis: Scaling-Up with a Quantum Socket
Quantum Information

Synopsis: Scaling-Up with a Quantum Socket

A three-dimensional mesh of wires could connect large arrays of superconducting qubits in a quantum computer. Read More »

More Articles