Thursday, August 6, 2020

Colorado Physicist Receives Acclaim (and NSF Funding) For Quantum Entanglement Research

Photo of Optical clock in Jun Ye's lab, and depiction of a quantum engineering application.

The news that Jun Ye of the University of Colorado has received a $25 million NSF (National Science Foundation) grant to fund a new center to study quantum systems  is welcomed by the whole CU system and all Coloradans.  It reinforces the fact that our state is at the forefront of modern science and technology.

Prof. Ye is based at JILA,

Originally standing for the 'Joint Institute for Astrophysics',  but which has now subsumed other physical sciences'  as  the center's  Research Topics page describes  (Though the acronym has been retained.)   As the summary in the above link describes it, the work explores:

"scientific questions about the limits of quantum measurements and technologies, the design of precision optical and X-ray lasers, the fundamental principles underlying the interaction of light and matter, the role of quantum physics in chemistry and biology, and the processes that have governed the evolution of the Universe for nearly 14 billion years."

As for Prof. Ye, he is a fellow at JILA and will now be conducting intensive investigations into quantum systems, how they interact and how they can be applied to the real world.  A special area of focus will be quantum entanglement.  This is a phenomenon in which two or more quantum particles become so fundamentally connected that anything done to one impacts the others.

Physicist Morgan Miller, quoted in Science News in 2011, affirmed that: "entanglement should be present in pretty much any situation with a lot of particles interacting with each other."    Most physics' arguments, however, take the view that quantum level entanglement is a bad thing for quantum computing. After all, if the quantum particles that are the basis for one's Q-computer become "entangled" with quantum particles outside then it is possible for information leakage and lost security.

At the heart of quantum entanglement is quantum nonlocality, one of the primary properties of entanglement.  It was physicist Alain Aspect who first conducted the experiment to show quantum nonlocality in a convincing way.  

Alain Aspect and his colleagues at the University of Paris, set up an arrangement as sketched below.  In these experiments, the detection of the polarizations of photons was the key. These were observed with the photons emanating from a Krypton-Dye laser and arriving at two different analyzers, e.g.

(P1) A1 
¯| <------D------> |­ A2 (P2)


Here, the laser device is D, and the analyzers (polarization detectors) are A1 and A2 along with two representative polarizations given at each, for two photons P1 and P2. The results of these remarkable experiments disclosed apparent and instantaneous connections between the photons at A1 and A2. In the case shown, a photon (P1) in the minimum (0) intensity polarization mode, is anti-correlated with one in the maximum intensity (1) mode.  

Assume twenty successive detections are made and we obtain at the respective analyzers (where a ‘1’ denotes spin  +1/2 detection and ‘0’ spin  (-1/ 2):

A1:   1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0

A2:   0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

On inspection, there is a 100% anti-correlation (i.e. 100% negative correlation) between the two and an apparent nonlocal connection. In practice, the experiment was set out so that four (not two - as shown) different orientation 'sets' were obtained for the analyzers. These might be denoted: (A1,A2)I, (A1,A2)II, (A1,A2,)III, and (A1,A2)IV.
 Each result is expressed as a mathematical (statistical) quantity known as a 'correlation coefficient'.  The results from each orientation were then added to yield a sum S:

S = (A1,A2)I + (A1,A2)II + (A1,A2,)III + (A1,A2)IV

 In his (1982) experiments, Aspect determined the sum with its attendant indeterminacy to be:   S = 2.70 ±  0.05 and in so doing experimentally validated Bell’s Inequality.  In so doing quantum nonlocality was demonstrated.  Below,  Alain Aspect gives a one minute description of quantum entanglement and nonlocality for a lay person:

As for physicist Jun Ye, the challenge for him and his team is to "harness quantum mechanical waves and ascertain what engineering and other applications are forthcoming." While the funding lasts, the program will operate under the tag: 'Quantum Systems Through Entangled Science and Engineering  - or Q-SEnSE - for short.  It will also bring together experts from Los Alamos, Sandia Laboratories and the National Bureau of Standards & Technology.

Beyond applying quantum physics to other disciplines such as engineering, the center will train students to do the same work.  In the words of Cindy Regal - a CU Professor and JILA researcher - a primary goal will be to "create a quantum -ready work force".

I have no doubt she, the Q-SEnSE team and professor Jun Ye will succeed.

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