Focus: Beam Up an Electron

Published February 6, 2004  |  Phys. Rev. Focus 13, 6 (2004)  |  DOI: 10.1103/PhysRevFocus.13.6

Proposal for Production and Detection of Entangled Electron-Hole Pairs in a Degenerate Electron Gas

C. W. J. Beenakker, C. Emary, M. Kindermann, and J. L. van Velsen

Published October 1, 2003
Figure 1
Physics Today 49, 22 (1996), copyright AIP

Quantum connection. A leaky barrier between puddles of electrons may provide the entanglement needed to teleport electrons within a solid. Previously only photons have been teleported.

Science fiction characters routinely beam to new worlds, but in real life only photons–particles of light–have been “teleported,” exploiting a bizarre quantum mechanical property called entanglement. Past proposals for teleporting particles of matter have involved isolated electrons and exotic devices. In the 3 October and 6 February issues of PRL, however, researchers suggest a way to entangle and teleport electrons in a solid, using a device that’s already commonly studied in physics labs. It would also open new possibilities for creating powerful quantum computers.

One fantastic result of quantum mechanics is that if two particles emerge from a single process, measuring one can affect the other long after they separate. Such entangled particles should arise from splitting isolated electron pairs [1] but this effect hasn’t been clearly observed yet, in part because the structures are hard to make. On the other hand, researchers routinely measure electrons within the “electron sea” in solids, but they haven’t had a good way to observe entanglement and teleportation on particles extracted from the sea.

To create entanglement in a solid, Carlo Beenakker, Marcus Kindermann, and their colleagues at the University of Leiden in the Netherlands propose in their October paper to use electrons added to a region of semiconductor. The entangler would consist of two such regions with a thin barrier between them. Occasionally an electron would sneak through the barrier, leaving behind an entangled “hole” with precisely matched properties. The researchers propose using an arrangement of electrons that has been used for other types of experiments in the past. The so-called quantum Hall state consists of two-dimensional sheets of electrons at low temperatures and high magnetic fields, and probing and manipulating it is “absolutely routine,” Beenakker says.

Now Beenakker and Kindermann suggest connecting two of their entanglers, so that the electron from one annihilates–or “fills in”–the hole from the other. The annihilated electron would then disappear into the electron sea, but its quantum state would be preserved in the surviving electron because of the entanglement. Although photons have been teleported over kilometers, the researchers will be happy to transfer the electron’s state a few micrometers.

But before attempting teleportation, experimenters should demonstrate entanglement, says Beenakker. “Entanglement is the fuel; teleportation is an application that consumes the fuel.” Even that won’t be easy because only a few electrons will sneak through the barrier. Still, Beenakker says, ”I’m willing to bet someone will do this in the next couple of years.”

Daniel Loss of the University of Basel in Switzerland questions whether electrons can survive even the short time needed for annihilation without forgetting the orbital part of their quantum state, which is essential to entanglement. Loss and his colleagues have focused on entanglement of only the spin component of the electrons’ quantum states [2] which he says will survive longer.

Beenakker and his colleagues hope electron teleportation can be used in future superfast quantum computers. To do this, the teleported signal would have to be strong enough to affect other devices, says David DiVincenzo of IBM in Yorktown Heights, New York. In contrast, Beenakker’s scheme appears to be “inherently a one-pass approach.” But he says the work is “part of the learning process” that may eventually make quantum computing possible.

–Don Monroe


References

  1. “Quantum Entanglement in Carbon Nanotubes, ” C. Bena, et al., Phys. Rev. Lett. 89, 037901 (2002); described in Phys. Rev. Focus 9, story 33 (2002).
  2. “Dynamical Coulomb Blockade, Spin-Entangled Electrons, ” P. Recher, and D. Loss, Phys. Rev. Lett. 91, 267003 (2003).