Beyond the operator algebra—To be nonlocal realism of quantum mechanics
Citation: Z. H. Zhu, Beyond the operator algebraTo be nonlocal realism of quantum mechanics, Sci. ChinaPhys. Mech. Astron.
Beyond the operator algebraTo be nonlocal realism of quantum mechanics
ZhiHan Zhu 0
0 Wang DaHeng Collaborative Innovation Center for Science of Quantum Manipulation & Control, Heilongjiang Provincial Key Laboratory of Quantum Manipulation & Control, Harbin University of Science and Technology , Harbin 150080 , China
•News & Views• . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . May 2018 Vol. 61 No. 5: 050331 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .https://doi.org/10.1007/s1143301891638

In 1905, Albert Einstein presented his milestone theory of
photons in his paper titled “On a Heuristic Viewpoint
Concerning the Production and Transformation of Light” based
on Max Planck’s blackbody radiation theory. The
groundbreaking theory successfully solved the paradox between
Maxwell’s wave theory of light and the experimental finding
on photoelectric effect, propelling the concept of
waveparticle duality and granting Einstein with his solo Nobel Prize
in 1921. Later, a group of physicists and mathematicians
developed a wavefunction formulation based on operator
algebra to describe quantum theory. This powerful
mathematical abstraction, the greatest theoretical invention in
human history, enables us to calculate and predict physical
process in the microscopic world that people cannot
intuitively understand, such as atomic energy levels, electron
tunneling, and photon trajectories. Through this drastic
paradigm shift, using wave theory to describe a particle
system, the first quantum revolution was directly produced,
laying the foundation of modern science and technology.
This shift, however, posed a profound question about
abstraction and reality, i.e., how to understand a dynamical
process on Hilbert space, especially for cases involving the
concept of superposition [
1
].
Are quantum states real? Today, nearly a century after the
birth of quantum mechanics, a second quantum revolution is
occurring [
2
] and the theory is extending into more general
regimes [
3
]; however, this old question persists. Bohr and
Schrödinger, representatives of the Copenhagen
interpretation, first may have thought a quantum particle really existed
in the form of its wavefunction. However, when Einstein,
Podolsky, and Rosen [
4
] showed that the cost of reality
requires a superluminal connection between two real systems,
Bohr and Schrödinger had to abandon that idea and
concluded that no elementary phenomenon is a phenomenon
until it is a registered phenomenon. Despite this, Einstein
insisted that physics should look for “really existing objects”
or to be local realism theory.
Over the next few decades, the nonlocal property of the
quantum world was repeatedly verified via experiments,
while the debate on reality always was a controversial topic.
In various delayedchoice experiments dedicated to this topic
[
5
], Copenhagen interpretation claimed that the photons
passing through the double slits have no definite nature until
they are measured and that wavefunctions provide only ‘‘a
catalog of knowledge”. In contrast, based on Einstein’s
famous query, ‘‘Do you really think the moon is not there if
you are not looking at it?” the determinists argued that the
past of photons should be realistic and deterministic prior to
the detection. Despite the results obtained 5 years ago in
various delayedchoice experiments seem to have rejected
the realistic interpretation, the recently observed
waveparticle superposition and disconnected propagation history
make the longstanding debate more intense [
6,7
]. Owing to
© Science China Press and SpringerVerlag GmbH Germany 2018 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . phys.scichina.com link.springer.com
2. . . . . . . . . . . . . . . . . . . . . . Z. H. Zhu,
May (2018) Vol. 61 No. 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0503312
the recent advance in science of structured light [
8,9
], the
new finding of the subluminal feature of twisted light enables
us to see the real past of photons after being registered;
consequently, the nonlocal reality of the quantum world was
finally confirmed in 2017 [
10,11
].
Almost the same time, Long et al. [
12
] from Tsinghua
University reported an encounterdelayedchoice (EDC)
experiment based on the idea of realistic interpretation of a
wavefunction in quantum mechanics, in which the
nonlocality and reality of the wavefunction is verified. More
interestingly, in the EDC experiment, by inserting the second
beam splitter (BS) of a MachZehnder interferometer when
the two sub waves (pulses) converge in the middle, first, a
pathsuperposed photon (wave nature) partially (or weakly)
collapses into distinguishablepath bases (particle nature);
second, it is measured with an identicalpath base (wave
nature). That is to say, photons can first behave as a particle
and then behave as a wave. This staggering result indicates
that the evolution of the whole system is deterministic
through the time axis. Specifically, a photon is first converted
into a superposition of two sub waves via BS1; then, the
photon weakly couples with the experimental apparatus and
the two sub waves together evolve into a collapseornot
superposition state when the front part of the wave pulse is
detected in particle nature; lastly, the collapseornot
superposition is observed in the wave nature when BS2 is
inserted.
More remarkably, in addition to the nonlocal realism, the
deterministic evolution history revealed in this brilliant work
deepened our understanding in the complementary concepts
of abstraction and reality. The results indicate that the
quantum states described by wavefunctions are real and that
the abstractreal boundary in the physical world is blurry.
Namely, start now, it is more valuable to ask whether we live
in Hilbert space rather than to doubt to be or not to be real.
1 C. P. Sun , Physics 46 , 481 ( 2017 ).
2 J. P. Dowling , and G. J. Milburn , Philos. Trans. R. Soc. A 361 , 1655 ( 2003 ).
3 C. M. Bender , D. C. Brody , and H. F. Jones , Phys. Rev. Lett . 89 , 270401 ( 2002 ).
4 A. Einstein , B. Podolsky , and N. Rosen , Phys. Rev . 47 , 777 ( 1935 ).
5 X. Ma , J. Kofler, and A. Zeilinger , Rev. Mod. Phys . 88 , 015005 ( 2016 ), arXiv: 1407 . 2930
6 J. S. Tang , Y. L. Li , X. Y. Xu , G. Y. Xiang , C. F. Li , and G. C. Guo , Nat. Photon 6 , 600 ( 2012 ).
7 A. Danan , D. Farfurnik , S. BarAd , and L. Vaidman , Phys. Rev. Lett . 111 , 240402 ( 2013 ).
8 F. Bouchard , J. Harris , H. Mand , R. W. Boyd , and E. Karimi , Optica 3 , 351 ( 2016 ).
9 D. Giovannini , J. Romero , V. Potoček , G. Ferenczi , F. Speirits , S. M. Barnett , D. Faccio , and M. J. Padgett , Science 347 , 857 ( 2015 ), arXiv: 1411 . 3987
10 Z. Y. Zhou , Z. H. Zhu , S. L. Liu , Y. H. Li , S. Shi , D. S. Ding , L. X. Chen , W. Gao , G. C. Guo , and B. S. Shi , Sci. Bull . 62 , 1185 ( 2017 ).
11 G. L. Long , Sci. Bull . 62 , 1355 ( 2017 ).
12 G. L. Long , W. Qin , Z. Yang , and J. L. Li , Sci. ChinaPhys. Mech. Astron . 61 , 030311 ( 2018 ).