Quantum sensor's advantages survive entanglement breakdown

Quantum sensor’s advantages survive entanglement breakdown
In the researchers' new system, a returning beam of light is mixed with a locally stored beam, and the correlation of their phase, or period of oscillation, helps remove noise caused by interactions with the environment. Credit: Jose-Luis Olivares/MIT

The extraordinary promise of quantum information processing—solving problems that classical computers can't, perfectly secure communication—depends on a phenomenon called "entanglement," in which the physical states of different quantum particles become interrelated. But entanglement is very fragile, and the difficulty of preserving it is a major obstacle to developing practical quantum information systems.

In a series of papers since 2008, members of the Optical and Quantum Communications Group at MIT's Research Laboratory of Electronics have argued that optical systems that use entangled light can outperform classical optical systems—even when the breaks down.

Two years ago, they showed that systems that begin with entangled light could offer much more efficient means of securing optical communications. And now, in a paper appearing in Physical Review Letters, they demonstrate that entanglement can also improve the performance of optical sensors, even when it doesn't survive light's interaction with the environment.

"That is something that has been missing in the understanding that a lot of people have in this field," says senior research scientist Franco Wong, one of the paper's co-authors and, together with Jeffrey Shapiro, the Julius A. Stratton Professor of Electrical Engineering, co-director of the Optical and Quantum Communications Group. "They feel that if unavoidable loss and noise make the light being measured look completely classical, then there's no benefit to starting out with something quantum. Because how can it help? And what this experiment shows is that yes, it can still help."

Phased in

Entanglement means that the physical state of one particle constrains the possible states of another. Electrons, for instance, have a property called spin, which describes their magnetic orientation. If two electrons are orbiting an atom's nucleus at the same distance, they must have opposite spins. This spin entanglement can persist even if the electrons leave the atom's orbit, but interactions with the environment break it down quickly.

In the MIT researchers' system, two beams of light are entangled, and one of them is stored locally—racing through an optical fiber—while the other is projected into the environment. When light from the projected beam—the "probe"—is reflected back, it carries information about the objects it has encountered. But this light is also corrupted by the environmental influences that engineers call "noise." Recombining it with the locally stored beam helps suppress the noise, recovering the information.

The local beam is useful for noise suppression because its phase is correlated with that of the probe. If you think of light as a wave, with regular crests and troughs, two beams are in phase if their crests and troughs coincide. If the crests of one are aligned with the troughs of the other, their phases are anti-correlated.

But light can also be thought of as consisting of particles, or photons. And at the particle level, phase is a murkier concept.

"Classically, you can prepare beams that are completely opposite in phase, but this is only a valid concept on average," says Zheshen Zhang, a postdoc in the Optical and Quantum Communications Group and first author on the new paper. "On average, they're opposite in phase, but quantum mechanics does not allow you to precisely measure the phase of each individual photon."

Improving the odds

Instead, interprets phase statistically. Given particular measurements of two photons, from two separate beams of light, there's some probability that the phases of the beams are correlated. The more photons you measure, the greater your certainty that the beams are either correlated or not. With entangled beams, that certainty increases much more rapidly than it does with classical beams.

When a probe beam interacts with the environment, the noise it accumulates also increases the uncertainty of the ensuing phase measurements. But that's as true of classical beams as it is of entangled beams. Because entangled beams start out with stronger correlations, even when noise causes them to fall back within classical limits, they still fare better than classical beams do under the same circumstances.

"Going out to the target and reflecting and then coming back from the target attenuates the correlation between the probe and the reference beam by the same factor, regardless of whether you started out at the quantum limit or started out at the classical limit," Shapiro says. "If you started with the quantum case that's so many times bigger than the classical case, that relative advantage stays the same, even as both beams become classical due to the loss and the noise."

In experiments that compared optical systems that used entangled light and classical light, the researchers found that the systems increased the signal-to-noise ratio—a measure of how much information can be recaptured from the reflected probe—by 20 percent. That accorded very well with their theoretical predictions.

But the theory also predicts that improvements in the quality of the optical equipment used in the experiment could double or perhaps even quadruple the signal-to-noise ratio. Since detection error declines exponentially with the signal-to-noise ratio, that could translate to a million-fold increase in sensitivity.

"This is a breakthrough," says Stefano Pirandola, an associate professor of computer science at the University of York in England. "One of the main technical challenges was the experimental realization of a practical receiver for quantum illumination. Shapiro and Wong experimentally implemented a quantum receiver, which is not optimal but is still able to prove the quantum illumination advantage. In particular, they were able to overcome the major problem associated with the loss in the optical storage of the idler beam."

"This research can potentially lead to the development of a quantum LIDAR which is able to spot almost-invisible objects in a very noisy background," he adds. "The working mechanism of quantum illumination could in fact be exploited at short-distances as well, for instance to develop non-invasive techniques of quantum sensing with potential applications in biomedicine."

Explore further

New research signals big future for quantum radar

More information: "Entanglement's Benefit Survives an Entanglement-Breaking Channel." journals.aps.org/prl/abstract/ … ysRevLett.111.010501
Journal information: Physical Review Letters

This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.

Citation: Quantum sensor's advantages survive entanglement breakdown (2015, March 9) retrieved 18 October 2019 from https://phys.org/news/2015-03-quantum-sensor-advantages-survive-entanglement.html
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Mar 09, 2015
The working mechanism of quantum illumination could in fact be exploited at short-distances as well, for instance to develop non-invasive techniques of quantum sensing with potential applications in biomedicine.

Is he claiming it may be necessary to consider the sun's biological energy as a source of amino acid substitutions that differentiate the cell types of all individuals of all species via fixation in the context of the physiology of their nutrient-dependent reproduction?

If so, I believe he may be challenging theories about mutations and evolution like this one:
"...genomic conservation and constraint-breaking mutation is the ultimate source of all biological innovations and the enormous amount of biodiversity in this world." http://www.amazon...99661731

I would like someone who understands the biophysically constrained epigenetic effects of anti-entropic light to address such claims. Is anyone not afraid to do so?

Mar 09, 2015
This comment has been removed by a moderator.

Mar 09, 2015
Better explanation of quantum entanglement I found at


Mar 09, 2015
This comment has been removed by a moderator.

Mar 10, 2015
George Ellis is well-qualified to link quantum physics to quantum biology via the anti-entropic effects of light-induced amino acid substitutions that stabilize the DNA in the organized genomes of species from microbes to man.

He co-authored "Top-down causation: an integrating theme within and across the sciences?"http://rsfs.royal...abstract

Excerpt: The papers by Jaeger (microbiology) and Noble (physiology) are strong steps forward in this regard. This is perhaps the area where most needs to be done, across the board in all domains. Areas where striking progress is being made in this regard are epigenetics [22] and social neuroscience [23].

A month later, I published "Human pheromones and food odors: epigenetic influences on the socioaffective nature of evolved behaviors." in Socioaffective Neuroscience & Psychology. http://www.ncbi.n...24693349

I linked the physiology of microbes to biodiversity, sans mutations.

Mar 10, 2015

I linked the physiology of microbes to biodiversity, sans mutations.

You didn't link anything.

You did write a bunch of Creationist gibberish.

Mar 10, 2015
The nutrient-dependent physiology of reproduction is controlled by the metabolism of nutrients to species-specific pheromones in species from microbes to man. As George Ellis has also clearly indicated, that fact is not Creationist gibberish.

For other examples of biologically-based cause and effect that link the sun's biological energy to RNA-mediated cell type differentiation via the biophysically constrained chemistry of protein folding see https://www.faceb...ediated/ and/or RNA-mediated.com

Mar 10, 2015
I would like someone who understands ... Is anyone not afraid to do so?
you will simply ignore ANY evidence presented to you that doesn't agree with your preconceived notions and beliefs, or your religious perspective, as demonstrated by ANON, Real and so many others

case in point: you've made claims that Dr. Extavour's studies supported your "model" UNTIL she said you were WRONG
just because we provide evidence that nutritional conditions play a role, this does not negate a role for mutations. Indeed, in that very same paper, we provide evidence that heritable differences in the genome sequences between Drosophila species, in other words, mutations, ALSO play a role in the evolution of the trait we are studying.

So Kohl is mistaken if he is claiming that my study (or Rich Lenski's work) provide evidence AGAINST the role of mutations in evolution
you're DEBUNKED already

Mar 10, 2015
Also see: Quantum Criticality at the Origin of Life http://arxiv.org/...02.06880

I think that senior author, Stuart A. Kauffman, may have been the first to mention the fact that:

"...our scientific understanding of reality is radically incomplete, and that some sort of anti-entropy, order-generating force remains to be discovered."


Mar 11, 2015
senior author, Stuart A. Kauffman
i am surprised you posted Kauffman because if his views...
they are not only ANTI-god in the creationist description, but anti-KOHL as well
but not an omnipotent, omniscient, kind God in monotheistic sense at all.
Kauffman believes in MUTATIONS, just not in physical laws (as in PHYSICS and standard LAWS which are inviolate dictating certain parameters of the TOEvolution) See "No entailing laws" and "Prolegamonen."
But it is to be expected because he is NOT A PHYSICIST

he only believes Darwinian Evolution is incomplete... NOT that it is completely wrong, like YOU are claiming, idiot boy jk!

and EVERY SCIENTIST I'VE EVER MET thinks that "our scientific understanding of reality is radically incomplete" so don't read into that anything that supports your stupidity, jk
IOW - it is NOT PROOF of a god/skyfaerie
it is simply an acknowledgement of ignorance on certain topics

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