Quantum filtering one bit at a time

Update (22/12/11):
Our paper has now been published in Physical Review Letters here.
Update (11/11/11):
Our paper has been accepted for publication in Physical Review Letters.

Today we submitted a paper on quantum filtering using a digitized weak measurement record:

“Quantum filtering one bit at a time”
Jason F. Ralph and Neil P. Oxtoby
(read the abstract and download from arXiv:1108.0823)

The classical analogue signal originating from diffusive weak measurement of a qubit (or two) is digitized into a single bit based on its sign (+/-).  We show that such a one-bit record (OBR) can be used to purify a single- or double-qubit, both with and without feedback control.  Quantum discord and classical correlations between a pair of qubits are also very well reproduced by the OBR.

The bottom line:
we have made a significant reduction in the data required to accurately reconstruct a quantum state with only minor reduction in the filter performance.


I recently visited Garmisch-Partenkirchen to participate in the 6th annual International Conference on the Physics of Dusty Plasmas.  The conference was excellent.  Full of very interesting talks and a decent social program, too.  See photos below.

I presented a poster at the conference, entitled “Tracking Compressed Dust”.  This extended my work on accurate determination/estimation of the physics of dusty plasma crystals and liquids.

Contact me for the PDF of my poster, or for more details on my work on state estimation and tracking in dusty plasmas.


New paper

Our group recently published a paper entitled “Molecular Dynamics Simulations of Dynamic Phenomena in Complex Plasmas” in IEEE Transactions on Plasma Science.

You can find out more by reading the abstract here.

SPIE in Orlando

I’ll be presenting a talk in Orlando, Florida (U.S.A.) at the SPIE conference “Signal and Data Processing of Small Targets 2010” on Tuesday, 6 April (the final talk of the day).
It’s in the Sensor Data and Information Exploitation program track of the “Defense, Security and Sensing” symposium.*

If you can make it there, come and say “g’day”. No doubt there’ll be time for some beer and physics afterwards.

Contact me for the slides from my talk. The title and abstract are below:

Tracking interacting dust: comparison of tracking and state estimation techniques for dusty plasmas

Neil Oxtoby, Jason F. Ralph, Dmitry Samsonov, Céline Durniak

Complex (dusty) plasmas are a convenient mesoscopic test-bed for exploring kinematics of microscopic systems in different phases (fluid-like, crystal-like). Micron-sized ‘dust’ grains within an ion-electron plasma interact via a screened Coulomb interaction. These dust-dust interactions are the principal effect in the observed particle dynamics. This work investigates the accuracy of measurement and tracking techniques in the presence of complex nearest-neighbour interactions and how modern state estimation methods can be used to monitor this complex system. The principal requirement is to simplify the tracking algorithms to reduce the computational costs without reducing the accuracy of the particle tracks.

*Wow, I love symposia!” – Philip J. Fry (Futurama).

Update: pics of the shuttle launch:

Video is available on You Tube: here.