Physicists build quantum amplifier with single artificial atom

May 25, 2010 By Lisa Zyga feature
Quantum amplification by an artificial atom. Part (a) shows a sketch of a three-level artificial atom in which population inversion can be created by pumping the atom from the ground state to the second excited state. Part (b) shows the spectroscopy of the three-level atom.

( -- By demonstrating how a single artificial atom can be used to amplify electromagnetic waves, physicists from Japan are opening up new possibilities for quantum amplifiers, which can be used in a variety of electronic and optical applications.

As a device that uses to amplify a signal, a quantum amplifier comes in many different forms. Perhaps the most well-known example is the laser, which uses the process of stimulated emission to emit photons from optically stimulated atoms. Like most quantum amplifiers, lasers use intra-atomic transitions with many atoms (or molecules) to achieve signal amplification, and the transition frequencies are not easily tunable.

One way to realize a quantum amplifier that is tunable and fully controllable is to create a system that uses only a single atom or molecule. However, single-atom quantum amplifiers have so far been very difficult to realize due to the fact that natural atoms can only be weakly coupled to the that they must amplify.

Now, researchers O.V. Astafiev and coauthors from NEC Nano Electronics Research Laboratories and RIKEN Advanced Science Institute, both in Ibaraki, Japan, have found a way to overcome this difficulty. In their new study, the researchers have demonstrated how a single artificial atom can be strongly coupled to the electromagnetic modes of open one-dimensional space, resulting in tunable and controllable electromagnetic wave amplification.

The quantum amplification is based on the ability to pump the three-state artificial atom from its ground state to the higher of its two excited states. To do this, the researchers applied microwave fields at a specific pumping frequency that propagated along a one-dimensional transmission line toward the point-like atom. The photons induced spontaneous emission from the atom, causing it to generate a scattered wave at a specific frequency, amplifying the overall signal.

“The key process is the preparation of population inversion (same as in lasers),” coauthor Abdufarrukh Abdumalikov from RIKEN told “Our atom has three discrete energy levels. We apply a microwave which excites it from the ground state to the second excited state. From the latter the atom relaxes partly to ground state and partly to first excited state. When the population of the first excited state is larger than that of the ground state we have a population inversion. Then we apply another microwave signal which we would like to amplify. It should be in resonance with the ground state - first excited state transition. It stimulates this transition and the atom emits a photon which adds up to the signal. The principle is the same as in lasers.”

The researchers calculated the maximal gain to be about 1.09, corresponding to an average of 109 emitted photons for every 100 incident photons. Abdumalikov explained that the maximum theoretical gain is 1.125, or 112.5 emitted photons for every 100 incident photons.

Overall, the amplification by a single artificial atom provides an example of an elementary quantum amplifier, which could be used as a building block for large-scale, tunable quantum amplifiers for various applications. In addition, the demonstration of single-atom quantum amplification could open up possibilities for developing new types of on-chip quantum amplifiers and other quantum devices, which could reveal novel quantum optical phenomena due to the devices’ strong coupling, tunability and controllability.

“This is the first work of this kind,” Abdumalikov said. “If we use many atoms we can obtain larger gain. Such amplifiers can be used in other research fields where low noise is needed. One such research field is an on-chip version of cavity quantum electrodynamics (QED) that is circuit QED.”

Explore further: Yale scientists bring quantum optics to a microchip

More information: O.V. Astafiev, et al. “Ultimate On-Chip Quantum Amplifier.” Physical Review Letters 104, 183603 (2010). Doi:10.1103/PhysRevLett.104.183603


Related Stories

Yale scientists bring quantum optics to a microchip

September 8, 2004

A report in the journal Nature describes the first experiment in which a single photon is coherently coupled to a single superconducting qubit (quantum bit or "artificial atom"). This represents a new paradigm in which quantum ...

Single Atom Quantum Dots Bring Real Devices Closer (Video)

January 27, 2009

( -- Single atom quantum dots created by researchers at Canada’s National Institute for Nanotechnology and the University of Alberta make possible a new level of control over individual electrons, a development ...

Could a quantum motor do work?

July 7, 2009

( -- Ever since the idea of a quantum world was discovered, physicists have been trying their best to create applications and uses that mirror the accomplishments of the classical world. However, due to the fact ...

From a classical laser to a 'quantum laser'

March 31, 2010

Rainer Blatt's and Piet Schmidt's research team from the University of Innsbruck have successfully realized a single-atom laser, which shows the properties of a classical laser as well as quantum mechanical properties of ...

Controlling the interaction between light and matter

April 30, 2010

( -- "One of the most exciting things about this is that it gives us nice, clean control over the interaction between light and matter," William Kelly tells "Our technique has the potential to give ...

Trapping giant Rydberg atoms for faster quantum computers

May 6, 2010

In an achievement that could help enable fast quantum computers, University of Michigan physicists have built a better Rydberg atom trap. Rydberg atoms are highly excited, nearly-ionized giants that can be thousands of times ...

Recommended for you

Test racetrack dipole magnet produces record 16 tesla field

November 30, 2015

A new world record has been broken by the CERN magnet group when their racetrack test magnet produced a 16.2 tesla (16.2T) peak field – nearly twice that produced by the current LHC dipoles and the highest ever for a dipole ...

Turbulence in bacterial cultures

November 30, 2015

Turbulent flows surround us, from complex cloud formations to rapidly flowing rivers. Populations of motile bacteria in liquid media can also exhibit patterns of collective motion that resemble turbulent flows, provided the ...

CERN collides heavy nuclei at new record high energy

November 25, 2015

The world's most powerful accelerator, the 27 km long Large Hadron Collider (LHC) operating at CERN in Geneva established collisions between lead nuclei, this morning, at the highest energies ever. The LHC has been colliding ...


Adjust slider to filter visible comments by rank

Display comments: newest first

May 25, 2010
This comment has been removed by a moderator.
May 25, 2010
This comment has been removed by a moderator.
not rated yet May 29, 2010
quantum amplifier ?
you mean, a one-atom laser for EM in the microwave regime, no?
not rated yet Jun 16, 2010
So my first post asking "What is an artificial atom?" was removed by the admins for "pointless verbiage." And they removed it almost a month after I posted it.

Good call, PhysOrg staff. Remove legitimate questions about articles but not the 100-post long pointless arguments about religion.

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.