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,  https://jila.colorado.edu/about/about-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:

PREVIEW

2:41

Prof. Alain Aspect Explains Quantum Entaglement

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.

Chinese Experiment Dramatically Demonstrates Quantum Entanglement

Artist's conception of Chinese ground station 'teleporting' photons to its Micius satellite

Nearly one year ago I cited work by Morgan  Mitchell and a team from the Institute of Photonic Sciences in Barcelona,  in Physical Review Letters . Their work described a specially prepared light beam that enabled the observation of individual photons in addition to charting the quantum links between them. Basically then, the Mitchell team confirmed the theoretical prediction that all the photons involved  exhibit some degree of entanglement and that the most strongly "entangled" would be pairs of photons striking the detectors at the same time.

According to Mitchell, quoted in Science News, "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 quantum computer become "entangled" (with quantum particles outside) then it is possible for information leakage and lost security.  However, the flip side of that is the view that entanglement can actually lead to an instantaneous, ultra-secure internet. This would be feasible if information encoded in one set of photons pops up instantaneously (and hence unhackably) in the corresponding set.

Now, Chinese quantum physicists have putatively demonstrated this feasibility in a recent experiment. The team from the University of Science and Technology of China announced barely 7 weeks ago that it had succeeded in splitting pairs of photons.  One of each split pair remained in the lab on Earth while the other member was beamed to China's Micius satellite, orbiting  300 miles above the Earth.  Most importantly, each photon "teleported" to the satellite remained entangled with its partner on Earth. An invisible connection hundreds of miles apart, if you will. (The accompanying diagram portrays this experiment).

A month earlier, in fact, the Chinese physicists showed that the teleportation worked in the opposite direction as they originated the splitting of photons on the Micius before sending them to separate receiving stations on Earth some 745 miles apart.  The word "incredible" doesn't even begin to describe the result.

Let's back up a bit: Einstein, Podolsky and Rosen (E-P-R) originally  imagined a quantum system (atom) which could be 'ruptured' such that two electrons were dispatched to two differing measurement devices. Each electron would carry a property called 'spin'. Since the atom had zero spin, this meant one would have spin (+ 1/2), the other (-1/2). The diagram below illustrates this, the atom being disrupted inside the box, with its opposing spin electrons sent to the left and right.

A1 (+ ½ ) <----------->(- ½ )A2

Orthodox quantum mechanics forbade the simultaneous measurement of a property (say different spin states) for the same system. If you got one, you could not obtain the other. This was a direct outcome of the Heisenberg Indeterminacy Principle which stated that simultaneous quantum measurements could not be made to the same precision.

The first ever hints of entanglement (and tests of Bell's theorem) actually emerged in experiments carried out in the early 1980s, for example by Alain Aspect and his colleagues at the University of Paris.  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.

Aside:  Polarization refers to that property whereby EM-radiation as it propagates can be confined say to one plane, or one rotation plane. If we say "circularly polarized" then the E-vector rotates through a full 360 degrees. If we say "linearly polarized" then it vibrates in one plane, e.g.

(A)
^
!
!
!
!

Or:

(B) < --------------------------------->----------------------------

Here, one might take (A) as the maximum intensity polarization mode and (B) as the minimum. 

Aspect et al on inspection of their data found there was 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.

Essentially, the basis for our modern conception of entanglement was laid. It thereby became theoretically possible for two particles to become connected in such a way that even if placed on opposite sides of the universe whatever happened to one of the particles would instantly be reflected in the behavior of the other. 

The photons split by the Chinese weren't on opposite sides of the universe, but they were hundreds of miles apart which is impressive enough. 

Historically, let's note that not all physicists have accepted the notion of "superluminal transport" which is what the instantaneous connections suggest. According to special relativity nothing moves faster than light, at c = 300,000 km/ second. Thus, if a pair of split photons instantaneously displays connections 300 or more miles apart it indicates faster than light transport.  That is, in the "teleportation" scenario,  the split photon leaving - say its twin on Earth- had to arrive at the Micius satellite at the same instant. This would have meant v >  c.

To get away from that inference, physicist David Bohm,  in his book Wholeness and the Implicate Order, proposed that the seemingly instantaneously connected particles - whether photons, atoms or electrons - are actually always connected at a higher dimensionality.  However, after the Chinese experiments, when physicist Alan Steinhardt was asked if such particles could be connected via another dimension, responded:  "Extra dimensions do potentially solve certain quantum quandaries, but I don't believe entanglement is one of them."

He might well be correct, and Bohm died before he was able to complete the experiment he designed (outlined in one of his papers) to test his stochastic theory of QM.

Should Undergrads Be Exposed To Modern Physics?

A Loyola University undergrad, ca. 1966, studying for a test on special relativity. The class used a text by Hugh D. Young entitled 'Fundamentals of Mechanics and Heat' (which I reviewed at Amazon) and included at least one chapter (14) on special relativity. 

That is perhaps the most that the majority of bright undergrads would be able to cope with even today.


An ongoing controversy in physics education is just how much modern physics today's undergrads should be exposed to. By definition, 'modern physics'  includes all the physics established since 1900, including: quantum theory, special and general relativity and some high energy particle physics (nature of quarks, neutrinos etc.)

The typical plaintive cry, to judge from occasional letters (say to Physics Today)  amounts to some variation on:

"Why must we be stuck in the tedious, boring physics of the 17th, 18th and 19th centuries? Why always Newton, Faraday and such instead of Bohr, Einstein and Schrodinger?  We want to be taught more of the modern physics less of the antiquated stuff!'

Thus, they are chagrined they're still being taught mostly Newtonian mechanics,  and 'old-style' Electricity and magnetism, thermal physics and only a little bit of special relativity.  What they don't say is that even that "little bit" of special relativity often poses problems.

So the question remains: can they really handle more? Most undergrads even at the top universities are simply not at the level they can grasp quantum mechanics or general relativity. Even Richard Feynman ('Feynman Lectures')  while conducting his famous first year course at Caltech, complained about the difficulty of getting quantum concepts over to many of the students.  Of course, there will always be the select few with plenty of mathematics and physics background for whom the content won't present huge problems. But make no mistake they're in the minority.

I still recall teaching a Calculus physics course for which the final chapter of the text assigned had significant quantum mechanics content, including:  the basic Schrodinger wave equation, quantum square well, atomic energy levels, eigenvalues, probability densities and how to compute expectation values. Attached below  is one problem which I worked out for the class:


But which only 1-2 of the class actually got. Most were stung by: a) not having the requisite mathematical ability (which makes one wonder how they managed to be allowed to move on from the earlier semesters) and b) not being able to conceptualize (despite numerous visual aids).


One of the visual aids which flummoxed them is shown below, including the first 3 wave functions for the H- atom(far left), the corresponding probability densities (middle) and the associated energy levels for an "infinite square well".


Basically, the possible energies of the particle, called energy levels, are quantized. The integer n used to designate them, is called the principal quantum number.

The state with lowest energy, n = 1, is called the ground state. The state with n = 2 is called the first excited state and so on.

There are n/2 de-Broglie waves capable of fitting into the well if the particle is in the nth quantum state.

At once the diagram captures the beauty and simplicity of quantum mechanics, in showing how energy is quantized in "jumps" as it is in the actual hydrogen atom.

In retrospect, the experience at Loyola with Hugh Young's presentation  of special relativity was perhaps at the limits of what a well prepared undergrad could understand.   For example, his derivation of the relativistic equation of energy (W) on pages 394, 395:

ò ^x2 _x1  dp/dt  dx = ò ^t2 _t1  (dp/dt)(dx/dt)  dt =

  ò ^t2 _t1  v(dp/dt)   dt  =  ò ^v2 _v1  v(dp/dv)  dv

W=   ò ^v2 _v1   v  d/dv [m_o v/ Ö (1 - v²/c² ] dv

The preceding equation for W applies since for relativistic momentum:

p  =  m_o v/ Ö (1 - v²/c² )

I argue the above is "at the limit" because of the calculus -based approach with which most undergrads would not be comfortable, even those who've taken AP Calculus.  More to the point, if one veers into quantum theory and general relativity, it doesn't get any easier.

This leaves us asking the question of whether there is an alternative solution or approach, specifically for those less able students who aren't attending Caltech, MIT or Harvard.  I believe there is and came away with one idea from a recent Readers Forum article ('How Black Holes Saved My Astronomy Course')  in Physics Today by Joseph Ribaudo..  Ribaudo - based at Utica College, New York- noted the struggle of his students to master the material  with most underperforming (averages in the "C range")  in his astronomy course.   He realized a large part of the problem was that  the existing astronomy textbooks were all too similar in their writing, content and design elements - and often way too mathematical. So he turned to Neil Degrasse Tyson's 'Death By Black Hole' as his central (core) text aided by "reading and writing assignments derived from popular and historical science publications".

Can a similar strategy be used to incorporate more modern physics into undergrad classical physics courses? I am confident this is feasible. Of course, the extent of integration of the modern physics material will hinge on the time allotted for the course or courses.  In most ('General Physics') courses, the modern physics is fit in at the very end - usually in one or two chapters featuring special relativity and some of the 'original' quantum mechanics, say of Bohr then Schrodinger.  At the maximum level of exposure students will be shown the use of the Schrodinger equation to solve for simple QM systems, say a particle in a box. This assumes, of course, the student has done some work in differential equations. (N.B. It is extremely rare for freshman and sophomore physics majors to take a dedicated modern physics course, far less a QM or Relativity course.)

But let's assume students are roughly at the math and abstraction level of  Ribaudo's astronomy class. What texts might supplement the approach to teach modern physics? I'd include the following:

'The Strange Story of the Quantum' - by Banesh Hofman (Dover, 1964)

'Thirty Years That Shook Physics' - by George Gamow (Dover, 1966)

'Relativity and Common Sense' -  by Herman Bondi (Dover, 1964)

'Sidelights on Relativity' - by Albert Einstein (Dover, 1954)

'The ABC of Relativity' - by Bertrand Russell (Signet, 1959)

 All of the above are eminently readable, and the math is at a minimum. Much of the math that is set out, such as in Bondi's book, is in the form of geometry from which simple derivations of the principles are shown. Einstein's book is terrific in providing an understanding at a non-math level by the master himself.

Ribaudo mentions in his article (p. 11)  setting one mid term exam question to the effect: "Discuss the value of reading 'Death By Black Hole' and whether you'd recommend this book to others".  The same sort of question might be asked of any of the books listed above.  In terms of how much contextual mathematics one's students can handle that has to be left to the instructor. For those who might wish to know some QM but minus all the math, Hoffman's book is probably best. For those who might wish to know some special relativity without the math, Russell's book is likely best. For those who are comfortable with plane geometry and some algebra,  Gamow's book is ideal for QM, and Bondi's ditto for special relativity.

If instructors in special relativity wish to get into more problem solving and math exposure - still largely at the intermediate algebra level (with a tiny bit of differential calculus)-  my own text: 'Modern Physics: Notes, Problems and Solutions' is ideal, namely the first three chapters (pp. 1 -45).

Ribaudo also cites "reading and writing assignments" from popular science magazines (e.g. Discover) and this can also provide fertile material for modern physics. For example, asking students to read the excellent article on quantum entanglement in Discover (July/August, 2016, p. 60) and asking students how they might explain this to a friend. Or better, how they might explain it if they could go back in time and encounter Neils Bohr.

In the end, it is possible to present modern physics to undergrads, but it has to be tailored to their own math and abstraction abilities.  If this is done, and there is the time allotted to do it without having to rush, then both physics instructors and their students will be all the better for it. And we may see much less whining from the undergrads about being denied entry into the "modern stuff".

---------------------
Addendum:

The best modern physics text I've found for math proficient students - geared to freshman and sophomores - is 'Space, Time and Quanta: An Introduction to Contemporary Physics' by Robert Mills (1994).  In his Introduction,  Mills writes of the text being a "supplement to a more conventional course" or "designed for the physics side of an interdisciplinary course" - i.e. for other (non-physics) students, but don't believe it. The text is in fact perfect as a standalone, totally complete modern physics text - at least on a par with the analogous content in The Feynman Lectures.  The end of chapter problem sets are especially good, and I simply can't see any "interdisciplinary" student being able to get through them.  Hence, I believe Mills greatly underestimates the book's value as a teaching text for modern physics.

Quantum Entanglement's Manifestations Finally Measured

As noted in an earlier (Aug. 29)  post to do with  the role of consciousness in physics, I pointed out that at least some connections vis-a-vis quantum entanglement needed to be made before a serious empirical discussion could even commence. This has now evidently occurred as physicists have finally measured connections between pairs of photons within a macroscopic beam of light. These connections have been said to qualify as quantum entanglement and represent a step toward understanding how the rules of QM scale up to phenomena such as superconductivity, involving large numbers of particles.

Physicist Henry Stapp has noted that the neural dynamics of the human brain in the vicinity of synapses involve large numbers of particles, namely Ca++ ions which - on account of synaptic cleft dimensions (200-300 nm)-   can be treated in wave form.  The brain then, like a full quantum computer, can be regarded as subject to effects of quantum entanglement and exploring such manifestations could lead to insights into consciousness.

But first things first.  The experiment - to be published in Physical Review Letters - describes a specially prepared light beam that enables the observation of individual photons in addition to charting the quantum links between them. Basically then, the team from the Institute of Photonic Sciences in Barcelona, under Morgan Mitchell, confirmed the theoretical prediction that all the photons involved would exhibit some degree of entanglement and that the most strongly "entangled" would be pairs of photons striking the detectors at the same time.

According to Mitchell, quoted in Science News, "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.

In the case of Mitchell's team, while the study of entangled particles in superconductivity would have been ideal, the problems involved would have been formidable. (SCs are so densely packed with electrons that measuring even a small subset would have been extremely difficult. Imagine then the tandem problem of measuring entanglement to do with brain neurons.)

So, as a result, the Barcelona team confined attention to the much simpler macroscopic system of a "squeezed" beam of light.  Not physically squeezed, obviously, but rather transmitted through a crystal enabling the measurement of a particular property, in this case polarization.

Polarization refers to that property whereby EM-radiation as it propagates can be confined say to one plane, or one rotation plane. If we say "circularly polarized" then the E-vector rotates through a full 360 degrees. If we say "linearly polarized" then it vibrates in one plane, e.g.

^
!
!
!
!

Or:

<--------------------------------->----------------------------

Thus, Mitchell's Barcelona team filtered the beam of light and probed it with polarization detectors.  A click at the detector location indicated the arrival of a photon with a particular polarization. Any pairs traveling in tandem (and arriving simultaneously) had corresponding polarizations. I.e. horizontally polarized such as indicated in the lower sketch above.

Clearly, much more work has to be done, especially by way of confirmation, as well as extending the conclusions to other systems for greater generality. A case in point would be to convince skeptics like Prof. Timothy Ralph of University of Queensland, who doesn't accept that the Mitchell team's results are applicable for any phenomena other than "squeezed" light.

We shall see!