Synopsis: Quantum Pairs Walking

Researchers demonstrate quantum random walks of photon pairs that interact like bosons, fermions, or anything in between, which could be used to simulate other quantum systems.
Synopsis figure
L. Sansoni et al., Phys. Rev. Lett. (2012)

Harnessing quantum information could allow powerful computations that are inaccessible to classical systems. But many quantum features of a single particle simply reflect its wavelike aspects. Experiments in Physical Review Letters simultaneously manipulate pairs of particles, whose interlinked behavior cannot be emulated by classical waves. Linda Sansoni of Sapienza University of Rome, Italy, and her colleagues implemented the quantum version of a discrete random walk using photons in a centimeter-sized glass chip. They first focused intense laser pulses along chosen paths, which tweak the glass’s refractive index to create stable waveguides for later photons. Running two parallel waveguides alongside each other for about two millimeters gives a photon a 50/50 chance of jumping between them.

The team wrote an array of parallel waveguides that periodically came closer to their left or right neighbors. A photon launched into one waveguide could emerge in any of eight guides, depending on which jumps it made in the various interaction regions. But unlike the classical version of the random walk, the probabilities of different outcomes reflect the effects of quantum interference between different paths.

The researchers used beamsplitters to mimic both a “quantum coin” operation (whether a photon jumps) and the walker displacement. By launching pairs of photons whose polarization states were entangled, the researchers could reproduce all types of quantum interactions, from fermionlike repulsion to bosonlike attraction and anything in between. These results matched theoretical expectations, but the technique could be adapted to simulate other, less-well-understood quantum systems. – Don Monroe

Correction (6 January 2012): Paragraph 3, sentence 1, “The researchers used the vertical or horizontal polarization of the photons to encode a quantum degree of freedom, or “quantum coin,” which affects whether a photon jumps or not.” changed to “The researchers used beamsplitters to mimic both a “quantum coin” operation (whether a photon jumps) and the walker displacement.”


More Features »


More Announcements »

Subject Areas

Quantum InformationPhotonics

Previous Synopsis

Interdisciplinary Physics

Quantum Search for Elusive Numbers

Read More »

Next Synopsis

Related Articles

Viewpoint: Seeing Scrambled Spins
Atomic and Molecular Physics

Viewpoint: Seeing Scrambled Spins

Two experimental groups have taken a step towards observing the “scrambling” of information that occurs as a many-body quantum system thermalizes.   Read More »

Viewpoint: Type-II Dirac Fermions Spotted
Quantum Information

Viewpoint: Type-II Dirac Fermions Spotted

Three separate groups report experimental evidence of novel type-II Dirac quasiparticles, suggesting possible applications in future quantum technology. Read More »

Focus: <i>Image</i>—Honeycomb Diffraction

Focus: Image—Honeycomb Diffraction

Predictions of diffraction patterns for honeycomb photonic crystals were part of a comprehensive study of these structures that may be useful in nanoscale photonic devices. Read More »

More Articles