Synopsis: Measuring Nothing

Transitions in an atom can allow nondestructive measurement of the quantum vacuum state.
Synopsis figure
D. K. L. Oi et al., Phys. Rev. Lett. (2013)

Measuring empty space should be easy—just put a detector out and watch as it doesn’t do anything. In quantum mechanics, things are more subtle because empty space isn’t really empty and, typically, measuring a state destroys it, at least for subsequent measurements. As Daniel Oi at the University of Strathclyde, UK, and colleagues propose in Physical Review Letters, a single atom might be able to signal the presence or absence of the photon field vacuum state without otherwise altering it.

Oi et al. theoretically analyze a single three-level atom coupled to an optical cavity for storing photons. This atom has a special energy-level diagram—one excited state connected to two lower levels by separate transition paths—called a lambda system. One transition (call it A) is excited by a laser while the other (B) is only in contact with the cavity.

With suitable laser pulses, the atom can, in principle, be forced to evolve in a controllable way such that its state depends on the absence of a photon (vacuum) or presence of one or more photons in the cavity. If there is at least one photon in the cavity, and the atom starts in state B, it will end up in state A while pulling out the photon. Conversely, if the cavity is in a vacuum state (empty), the atom will stay in state B, and the cavity stays empty. This setup would allow multiple sequential operations, or could add new photons or extract one photon at a time from an existing cavity field. – David Voss


Announcements

More Announcements »

Subject Areas

Quantum Information

Previous Synopsis

Next Synopsis

Related Articles

Viewpoint: Photon Qubit is Made of Two Colors
Optics

Viewpoint: Photon Qubit is Made of Two Colors

Single particles of light can be prepared in a quantum superposition of two different colors, an achievement that could prove useful for quantum information processing. Read More »

Synopsis: Ten Photons in a Tangle
Quantum Information

Synopsis: Ten Photons in a Tangle

An entangled polarization state of ten photons sets a new record for multiphoton entanglement. Read More »

Synopsis: Quantum States Made with a Pluck
Quantum Information

Synopsis: Quantum States Made with a Pluck

A proposed method of generating phonon states for quantum applications uses a single electron trapped in a suspended carbon nanotube. Read More »

More Articles