Photons emitted by quantum dots can be made indistinguishable through quantum frequency conversion

December 20, 2012
The quantum frequency conversion system uses two pump lasers whose frequency difference is matched to the difference between the two input photon streams, causing the new photons from a nonlinear crystal to be emitted at exactly the same frequency.

(Phys.org)—An international collaboration led by researchers from the NIST Center for Nanoscale Science and Technology has demonstrated the ability to make photons emitted by quantum dots at different frequencies identical to each other by shifting their frequencies to match. This "quantum frequency conversion" is an important step for making solid-state, single photon sources, including quantum dots, more useful light sources for photonic quantum information science.

Quantum dot sources are desirable due to their high brightness, stability, and amenability to scalable fabrication technology, but frequency variations arising from nonuniform device fabrication have limited their usefulness. Previous research has focused on tuning the sources themselves, for example by inducing strain or by varying the electrical and optical fields surrounding the structures. In their new approach, the CNST-led team uses a fundamentally different approach – manipulating the photons after they are generated, rather than altering the sources.

As reported in the October 5, 2012 issue of Physical Review Letters and featured in the November issue of Physics Today, the experiment uses photons emitted from a semiconductor quantum dot at two different frequencies which are determined by two of the dot's different energy states. The team demonstrated that the photons can be converted to the same frequency, or color, using quantum , a process in which each a single photon stream is combined with light from a much stronger pump laser in a which outputs photons at a frequency that is the sum of the two inputs. Two pump lasers are used, with the frequency difference between them set to match the difference between the two input photon streams, causing the new photons to be at exactly the same frequency. An interference measurement is used to confirm that the frequency-converted photons have become identical. Since the current work uses relatively large nonlinear crystals for frequency conversion, future work will focus on implementing the conversion method in smaller and more scalable device architectures.

Explore further: This little light of mine: Changing the color of single photons emitted by quantum dots

More information: Ates, S. et al. Two-photon interference using background-free quantum frequency conversion of single photons emitted by an InAs quantum dot. Physical Review Letters 109, 147405 (2012).

Related Stories

Etched quantum dots shape up as single photon emitters

February 23, 2011

(PhysOrg.com) -- Like snowflakes or fingerprints, no two quantum dots are identical. But a new etching method for shaping and positioning these semiconductor nanocrystals might change that. What's more, tests at the National ...

Recommended for you

Important milestone reached on road to a redefined kilogram

June 21, 2016

In a secure vault in the suburbs of Paris, an egg-sized cylinder of metal sits in a climate-controlled room under three glass bell jars. It is the mass against which all other masses in the world are measured - by definition ...

Probing giant planets' dark hydrogen

June 23, 2016

Hydrogen is the most-abundant element in the universe. It's also the simplest—sporting only a single electron in each atom. But that simplicity is deceptive, because there is still so much we have to learn about hydrogen.

Why planes freeze

June 21, 2016

Pilots and safety officials worry about ice accumulating on the wings and tail of an aircraft flying during freezing rain. Abnormal ice buildup can disturb airflow to alter the physics of flight and lead to stalls, rolls ...

Understanding rogue ocean waves may be simple after all

June 21, 2016

An international team of scientists has developed a relatively simple mathematical explanation for the rogue ocean waves that can develop seemingly out of nowhere to sink ships and overwhelm oil platforms with walls of water ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.