Featured Research

from universities, journals, and other organizations

Toward new quantum possibilities: Seeing a photon without absorbing it

Date:
November 14, 2013
Source:
Max Planck Institute of Quantum Optics
Summary:
Scientists can detect an optical photon twice. Light is of fundamental importance. It allows us to see the world around us and record pictures of our environment. It enables communication over long distances through optical fibers. All current methods of detecting light share a common property: absorption and thus destruction of a photon. It has been a long-standing dream to be able to watch individual photons fly by without absorbing them. Scientists have now for the first time realized a device which leaves the photon untouched upon detection. This provides new possibilities for using single photons in quantum communication and quantum information processing.

Seeing a photon without absorbing it. Using a single atom trapped in an optical resonator, the presence of a reflected photon can be detected nondestructively.
Credit: MPQ, Quantum Dynamics Division

MPQ scientists can detect an optical photon twice.

Light is of fundamental importance. It allows us to see the world around us and record pictures of our environment. It enables communication over long distances through optical fibers. All current methods of detecting light share a common property: absorption and thus destruction of a photon. It has been a long-standing dream to be able to watch individual photons fly by without absorbing them. A team of scientists in the Quantum Dynamics Division of Prof. Gerhard Rempe at the Max-Planck-Institute of Quantum Optics has now for the first time realized a device which leaves the photon untouched upon detection.

In the experiment, the incoming photon is reflected off an optical resonator containing a single atom prepared in a superposition state. The reflection changes the superposition phase which is then measured to trace the photon. The new method opens up the perspective to dramatically increase the detection efficiency of single light quanta and has important implications for all experiments where photons are used to encode and communicate quantum information.

The key elements in the experiment are a single rubidium atom and an optical cavity. The latter is a resonator for light that is made of two highly-reflecting mirrors at a very small distance. The atom is trapped at the center of the cavity, where light forces strongly confine it in all three dimensions. It exhibits two different ground states, each characterized by its specific transition energy to the next excited state. To test the detector, the cavity is irradiated with a series of very faint lasers pulses that contain on average much less than a single photon.

In one of its ground states, the atom is off-resonant with both, the cavity and an impinging photon. In this case, the photon will enter the cavity, but not interact with the atom. Because of the special properties of the cavity, the photon will leave it on the same path it entered. In the other ground state, the atom is resonant with both, the cavity and the impinging photon. In this case, atom and cavity represent a strongly coupled system with properties distinctively different from those of the individual systems. In contrast to the first case, a photon, which is on resonance with the cavity, has no chance to get into it. Instead, it is reflected from the first mirror. In either case, the fragile light quantum is reflected rather than absorbed and destroyed.

"However, the photon has left its trace in the atom," Andreas Reiserer, doctoral student on the experiment and first author of the publication, explains. "The trick is that we prepare the atom in a superposition of the two ground states. The very moment the photon is reflected from the cavity, the resonant state experiences a phase shift relative to the off-resonant one. This phase shift can then be read out from the atom. In this way, the photon has survived its detection with its properties, for example its pulse shape or polarization, untouched."

The phase shift of the atomic state is detected using a well-known technique: "Loosely speaking, the atom lights up when probed after reflection of a photon," says Dr. Stephan Ritter, scientist at the experiment. In order to prove that the nondestructive detection works, the reflected photons are also registered by conventional photodetectors. "In this way, we detect the photon twice, which is impossible with destructive detectors alone. In our proof-of-principle experiment we have achieved a single-photon detection efficiency of 74 %, which is already more than the 60% of typical destructive detectors." Ritter says. "The achieved value is not fundamentally limited, but due to some imperfections that we can work on in the future."

The ability to observe single photons without destroying them or changing any of their degrees of freedom opens the perspective for a number of new experiments. A single photon can be detected repeatedly by combining several nondestructive devices. This also provides new possibilities for using single photons in quantum communication and quantum information processing. The successful transfer of a photon in a quantum network could be detected without destroying the fragile quantum information encoded in it. Based on the mechanism used for single-photon detection, it should also be possible to realize a deterministic, universal quantum gate between a reflected single photon and the single atom and even between two photons. Because quantum gates are the functional building blocks of a quantum computer, this is a long-standing dream in optical quantum computing.


Story Source:

The above story is based on materials provided by Max Planck Institute of Quantum Optics. Note: Materials may be edited for content and length.


Journal Reference:

  1. Andreas Reiserer, Stephan Ritter, and Gerhard Rempe. Nondestructive Detection of an Optical Photon. Science, 14 November 2013 DOI: 10.1126/science.1246164

Cite This Page:

Max Planck Institute of Quantum Optics. "Toward new quantum possibilities: Seeing a photon without absorbing it." ScienceDaily. ScienceDaily, 14 November 2013. <www.sciencedaily.com/releases/2013/11/131114141910.htm>.
Max Planck Institute of Quantum Optics. (2013, November 14). Toward new quantum possibilities: Seeing a photon without absorbing it. ScienceDaily. Retrieved October 20, 2014 from www.sciencedaily.com/releases/2013/11/131114141910.htm
Max Planck Institute of Quantum Optics. "Toward new quantum possibilities: Seeing a photon without absorbing it." ScienceDaily. www.sciencedaily.com/releases/2013/11/131114141910.htm (accessed October 20, 2014).

Share This



More Matter & Energy News

Monday, October 20, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Gulfstream G500, G600 Unveiling

Gulfstream G500, G600 Unveiling

Flying (Oct. 20, 2014) Watch Gulfstream's public launch of the G500 and G600 at their headquarters in Savannah, Ga., along with a surprise unveiling of the G500, which taxied up under its own power. Video provided by Flying
Powered by NewsLook.com
Japanese Scientists Unveil Floating 3D Projection

Japanese Scientists Unveil Floating 3D Projection

Reuters - Innovations Video Online (Oct. 20, 2014) Scientists in Tokyo have demonstrated what they say is the world's first 3D projection that floats in mid air. A laser that fires a pulse up to a thousand times a second superheats molecules in the air, creating a spark which can be guided to certain points in the air to shape what the human eye perceives as an image. Matthew Stock reports. Video provided by Reuters
Powered by NewsLook.com
Hey, Doc! Sewage, Beer and Food Scraps Can Power Chevrolet’s Bi-Fuel Impala

Hey, Doc! Sewage, Beer and Food Scraps Can Power Chevrolet’s Bi-Fuel Impala

3BL Media (Oct. 20, 2014) Hey, Doc! Sewage, Beer and Food Scraps Can Power Chevrolet’s Bi-fuel Impala Video provided by 3BL
Powered by NewsLook.com
What We Know About Microsoft's Rumored Smartwatch

What We Know About Microsoft's Rumored Smartwatch

Newsy (Oct. 20, 2014) Microsoft will reportedly release a smartwatch that works across different mobile platforms, has a two-day battery life and tracks heart rate. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins