Experiment suggests it might be possible to control atoms entangled with the light they emit by manipulating detection

May 12, 2016 by Diana Lutz, Washington University in St. Louis
The atom's paths through state space charted over time as it decays to its ground state due to spontaneous emission of light. Credit: Kater Murch

Flick a switch on a dark winter day and your office is flooded with bright light, one of many everyday miracles to which we are all usually oblivious.

A physicist would probably describe what is happening in terms of the particle nature of light. An atom or molecule in the fluorescent tube that is in an excited state spontaneously decays to a lower energy state, releasing a particle called a . When the photon enters your eye, something similar happens but in reverse. The photon is absorbed by a molecule in the retina and its energy kicks that molecule into an excited state.

Light is both a particle and a wave, and this duality is fundamental to the physics that rule the Lilliputian world of atoms and . Yet it would seem that in this case the wave nature of light can be safely ignored.

Kater Murch, assistant professor of physics in Arts & Sciences at Washington University in St. Louis, might give you an argument about that. His lab is one of the first in the world to look at with an instrument sensitive to the wave rather than the particle nature of light, work described in the May 20th issue of Nature Communications

. His experimental instrument consists of an (actually a superconducting circuit with two states, or energy levels) and an interferometer, in which the electromagnetic wave of the emitted light interferes with a reference wave of the same frequency.

This manner of detection turns everything upside down, he said. All that a photon detector can tell you about spontaneous emission is whether an atom is in its or its ground state. But the interferometer catches the atom diffusing through a quantum "state space" made up of all the possible combinations, or superpositions, of its two energy states.

This is actually trickier than it sounds because the scientists are tracking a very faint signal (the electromagnetic field associated with one photon), and most of what they see in the interference pattern is quantum noise. But the noise carries complementary information about the state of the artificial atom that allows them to chart its evolution.

In spontaneous emission, wave detection gives you more information than particle detection, as physicist Kater Murch of Washington University in St. Louis explains in this animation he drew and narrated. Credit: Kater Murch

When viewed in this way, the artificial atom can move from a lower energy state to a higher energy one even as its follows the inevitable downward trajectory to the ground state. "You'd never see that if you were detecting photons," Murch said.

So different detectors see spontaneous emission very differently. "By looking at the wave nature of light, we are able see this lovely diffusive evolution between the ," Murch said.

But it gets stranger. The fact that an atom's average excitation can increase even when it decays is a sign that how we look at light might give us some control over the atoms that emitted the light, Murch said.

This might sound like a reversal of cause and effect, with the effect pushing on the cause. It is possible only because of one of the weirdest of all the quantum effects: When an atom emits light, quantum requires the light and the atom to become connected, or entangled, so that measuring a property of one instantly reveals the value of that property for the other, no matter how far away it is.

Or put another way, every measurement of an entangled object perturbs its entangled partner. It is this quantum back-action, Murch said, that could potentially allow a light detector to control the light emitter.

"Quantum control has been a dream for many years," Murch said. "One day, we may use it to enhance fluorescence imaging by detecting the in a way that creates superpositions in the emitters.

"That's very long term, but that's the idea," he said.

Explore further: Superfast light source made from artificial atom

More information: M. Naghiloo et al, Mapping quantum state dynamics in spontaneous emission, Nature Communications (2016). DOI: 10.1038/ncomms11527

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Hyperfuzzy
1.7 / 5 (11) May 12, 2016
Really?
wizardo
1.7 / 5 (11) May 12, 2016
Our blind physicists again...
"...requires the light and the atom to become connected..."
So they are connected! See the light?
https://www.youtu...E427A7E6
Hyperfuzzy
1 / 5 (10) May 12, 2016
Really?

OK, Let's apply causality, there are a set of atoms, all made of just two particles, i..e is the center of a spherical field, the electron and the proton, neutron = some aggregation or superposition of these two points without scale, think these fields of each particle superimposed. It's only these two things, +&-, I see as the shape of space. Empty space or Euclidean Space, o any other manifestation cannot beat these guys, they're indestructible! If they move you notice. View them individually as a vortex of field & scale See the surface area of each sphere or simply search the harmonics in space and time. We have a differential measure of now and other points in time but scale that's where stuff really happens when peering smaller and smaller. We only know the motion of the center. Surely with only a few measurements may we define any point in space-time without the hocus pocus. oh so let's use this magic act it's over there so over here, the other glove!
compose
May 13, 2016
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compose
May 14, 2016
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compose
May 14, 2016
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compose
May 14, 2016
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Hyperfuzzy
1 / 5 (5) May 15, 2016
Don't get entangled in wrong thoughts! Space is simply the field and the singularities. Envision these without your macroscopic view. Make no stupid assumptions. Measure these. The singularity is waiting for you to understand. In fact I prefer just the field, while noting that the spherical fields are never created nor destroyed. These define everything. Get a masters degree in EE. Try to figure out the spatial centers. But don't waste your time trying to define it. Best effort is in the applications.
ChiefFartingDog
May 17, 2016
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Hyperfuzzy
not rated yet May 18, 2016
[note to the rational/civil posters]

See? The world didn't end because no one argued with the cranks. With nothing but crank crap on the thread, look at what a joke the page is! If we withheld all comment until the mods started dealing with the cranks, spammers and knee-jerk repetitive zealots the site would become like every other site that deals with that crap. I don't care who's paying whom or how, if the site becomes worthless, they've screwed the pooch.

Just look at the comments on this one. Tell me seriously that if every topic looked like this that they could continue to fail to deal with it. They couldn't. QED: Arguing with them is an important factor in the way the site has become.

How else do we define stupidity? The truth is typically diametrical!

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