Controlling the interaction between light and matter

Apr 30, 2010 By Miranda Marquit feature

(PhysOrg.com) -- "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 PhysOrg.com. "Our technique has the potential to give delicate and precise control over how artificial atoms interact with photons."

Kelly is with Raytheon BBN Technologies in Cambridge, Massachusetts. Along with a group of others in BBN’s Disruptive Information Processing Technologies division, and with scientists from the National Institute of Standards and Technology in Boulder, Colorado, Kelly took part in an experiment designed to observe superposition of states in a superconducting artificial atom. The group’s results are described in : “Direct Observation of Coherent Population Trapping in a Superconducting Artificial Atom.”

“In a , an atom is in only one energy level at a time, referred to as 0, 1, or 2. In , though, you get superposition states, in which the exact energy of the atom is not well defined,” Kelly explains. “In similar experiments, you see a lot of two-state interference. Our experiment, though, showed three-state interference. This is a new effect in these kinds of systems.”

To get this effect, Kelly and his colleagues worked with microwaves. “In atomic experiments, this type of thing is done with optical frequencies,” he says. “At room temperature it wouldn’t be feasible to use microwaves because of thermal noise, however at the temperatures we work at thermal noise is not a problem.”

The experiment involved super-cooling a tiny superconducting device, which acts as an artificial atom, to less than one tenth of a degree above . “You apply microwaves to this system, coupling an to the device, and use that to control the state the artificial atom is in. By sending in photons with energies that match the of the artificial atom, it is possible to get the artificial atom to transition states,” Kelly says.

One of the potential applications of this technique is in processing. “There are different possible platforms for realizing quantum information systems. Superconducting artificial atoms and photons are both candidates with their own advantages and disadvantages,” Kelly points out. “With this technique, we could potentially use the best of both worlds for quantum information processing.” He also points out that there has been a great deal of work done with optical switching, and that down the road this technique could lead to similar work with switching done with microwave frequencies. “We could use this as a sort of microwave transistor.”

On a fundamental level, this work could lead to increased knowledge of quantum systems, and the use of . “This is the first time we’ve seen coherence in three states in a manmade system,” Kelly says. “Additionally, there are interesting possibilities for using this to slow microwaves down, or even stop them.”

Further development is some while down the road, Kelly acknowledges, but there are some interesting opportunities available now. “We’re probably close to using this to demonstrate slow light,” he says. “However, there are a bunch of possible applications. With more study of this system, we should be able to figure out some new ways to advance technology.”

Explore further: And so they beat on, flagella against the cantilever

More information: W.R. Kelly, Z. Dutton, J. Schlafer, B. Mookerji, T.A. Ohki, J.S. Kline, and D.P. Pappas, “Direct Observation of Coherent Population Trapping in a Superconducting Artificial Atom,” Physical Review Letters (2010). Available online: link.aps.org/doi/10.1103/PhysRevLett.104.163601

4.6 /5 (19 votes)

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User comments : 15

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maxcypher
not rated yet Apr 30, 2010
Does anyone have more knowledge about the "superconducting device, which acts as an artificial atom"?
baudrunner
3 / 5 (2) Apr 30, 2010
Does anyone have more knowledge about the "superconducting device, which acts as an artificial atom
When a group of atoms are super-cooled into a Bose-Einstein condensate, they assume the characteristics of a single atom with a single deBroglie wave function.
Alizee
Apr 30, 2010
This comment has been removed by a moderator.
in7x
not rated yet Apr 30, 2010
"The term Artificial atom is commonly used to describe objects that have bound, discrete electronic states, as is the case with naturally occurring atoms. Semiconductor quantum dots are the most common example of artificial atoms, and are (square) 2D analogies for real atoms.

Artificial atoms, or quantum dots, are really made up of more than one atom, but are like single atoms in one important way: when you provide the right amount (or quanta) of energy, they will give off coloured light."
in7x
not rated yet Apr 30, 2010
Alizee
Apr 30, 2010
This comment has been removed by a moderator.
johanfprins
2 / 5 (3) May 01, 2010
When a group of atoms are super-cooled into a Bose-Einstein condensate, they assume the characteristics of a single atom with a single deBroglie wave function.

Is an "artificial atom" a structure with a nucleus and electron orbitals around it? This is hardly likely is it? I would say that a Bose-Einstein condensate of atoms must be a single macro-wave caused by the entanglement of all the original atoms during which process these atoms totally lose their identities. There cannot be any separate "particles" "within" such a wave.
Alizee
May 01, 2010
This comment has been removed by a moderator.
johanfprins
1 / 5 (1) May 01, 2010
... electrons in Rydberg atoms aren't forming typical orbitals - they revolve atoms along circular paths, instead.

How can an electron "revolve" along a circular path when its energy is less than its rest mass energy? Momentum, which is required to revolve along a circular path, can ONLY manifest when the electron has more energy than its rest mass energy.

All the electrons bound to a nucleus have less energy than their rest mass energy or else they have more energy than they will have when at rest at an infinite distance from the nucleus. So none of them can "revolve" around the nucleus!. They MUST all be stationary waves without any momentum.
Slotin
1 / 5 (2) May 01, 2010
How can an electron "revolve" along a circular path when its energy is less than its rest mass energy?
If you walk around, then the energy of yours is lower, then your rest mass energy, too - so I don't see any problem here.
Slotin
1 / 5 (3) May 01, 2010
This is how this stuff appears - Rydberg atom diameter is about 1 mm

http://www.physor...373.html
johanfprins
1 / 5 (1) May 02, 2010
If you walk around, then the energy of yours is lower, then your rest mass energy, too - so I don't see any problem here.


How is this possible? It violates the conservation of energy.

The example you give of the mm sized atom is not the same as a real atom; and should thus not be called an "atom". It is of course possible for an electron to circle a nucleus provided that its energy is larger than its rest mass energy. Thus although your example proves that this happens, it is not the way in which electron-orbitals form within real atoms. In real atoms the allowed electron states do not have any momentum at all. For this reason alone Bohr's model of the atom should be banned from physics text books.
croghan27
not rated yet May 02, 2010
Is there not some kind of irrational foofa-raw now being raised about some kind of military program what uses the Bohr model of the atom for its' symbol.

Apparently (I have only seen it briefly) it consists of a stylized Bohr atom with something coming around from the back in a swath.

The swath apparently to some, looks like an Islam crescent moon.
johanfprins
1 / 5 (2) May 02, 2010
@croqhan27
Not one of the electrons trapped around an atom as a stable "orbital" has momentum: Any picture of an atom showing these atoms moving, as had been done for nearly 100 years now, is claptrap!

A standing wave NEVER has momentum unless viewed from another inertial reference frame in which it is, owing to relativity, not a standing wave. This does not take away the fact that it IS STILL a standing wave within the reference frame relative to which it is standing.

The "orbitals" around a nucleus are standing (stationary) relative to the nucleus and can therefore not have momentum. The Bohr and Bohr-Sommerfeld quantization rules are thus claptrap!
ZeroX
not rated yet May 03, 2010
..in real atoms the allowed electron states do not have any momentum at all. For this reason alone Bohr's model of the atom should be banned from physics text books.
This is not true. Bohr's model is low energy approaximation of real atoms and as you can see, at the case of artificial or Rydberg's atoms or simple hydrogen atoms (which is still real atom) is pretty relevant. The orbital angular momentum of electrons indeed exists and it manifests itself by magnetic dipole moment - it's just quantized. The total magnetic dipole moment resulting from both spin and orbital angular momenta of an electron corresponds the total angular momentum. This is classicall stuff of every textbook.
johanfprins
1 / 5 (1) May 03, 2010
@Zerox,
You do not need an angular momentum to have a magnetic dipole moment. In fact what is done in our text books is to interpret the magnetic dipole moment as proof that there must be orbital momentum; which cannot be there since the kinetic energy of a atomic Schroedinger wave does not manifest within our three-dimensional space.

This is classicall stuff of every textbook.

So was Ptolemy's model until Copernicus and Galileo came along.

The fact is that no "particle" with mass can have momentum when its mass is less than its rest mass and for the electrons around an atom this is the case. The only way in which to get orbital momentum is to generate an electron around the nucleus that has energy larger than its rest mass. This has been done and should be called a Rutherford atom: Not a Rydberg atom. You cannot violate Einstein's Special Relativity as you are claiming is possible.
Alizee
May 07, 2010
This comment has been removed by a moderator.
Alizee
May 07, 2010
This comment has been removed by a moderator.
Alizee
May 07, 2010
This comment has been removed by a moderator.
johanfprins
1 / 5 (1) May 08, 2010
@Alizee,
You are again bombarding this forum with utter gobblydook and fairytales. You do not have to postulate "foam" and other nonsense which cannot be proved by experiment; since all physics from Galileo to Schroedinger becomes self-consistent as soon as one discards the probability interpretation for the intensity of a matter wave with an energy-interpretation:

The latter interpretation has through centuries been valid for ALL waves. The intensity of a matter wave MUST thus be its mass distribution and when you have a mass distribution you have a centre-of-mass. Therefore a moving wave can appear as if it is moving like a "particle" with all its mass concentrated at its centre of mass. This does not make it a "particle". Jupiter moves as if it is a "particle" with all its mass at its centre of mass but it is most definitely not a "point-particle".
Caliban
1 / 5 (2) May 08, 2010
In the article, Kelly makes mention of the classical physics model of energy states, and their designation as 0, 1, and 2.

Just speculation on my part, but I wonder will it be discovered that there are actually more -my guess would be 5- that are related energetically via wavelength/phase? You know- the "golden Ratio", and all

I have absolutely no data to back that up, but given particle/wave duality, and matter/energy equivalence, the notion keeps teasing the back of my mind.
Alizee
May 08, 2010
This comment has been removed by a moderator.