Delayed-choice Experiment
in Cavity QED
Rameez-ul-Islam
National Institute of Lasers and
Optronics, Islamabad.
Layout of the Talk
1. Introduction to Quantum Eraser
2. Cavity QED based Quantum Eraser
 Initial State
 Proposed Experimental Schematics
 Delayed-Choice, Asymmetric Erasing
 Distunguishability and Visibility: Tuneability
3. Conclusions
Introduction to Quantum Eraser
C
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Double Slit Experiment: Core Mystery of the
Quantum Theory
Feynman famously said: “The double-slit experiment has in it the heart
of quantum mechanics. In reality, it contains the only mystery”
How a particle
goes through
both the slits
simultaneously
!!
Double Slit Experiment and Which-Path Information
When we
observe………!!
Quantum Eraser: Newsweek, June 19, 1995, p. 68
Erasing Knowledge!
As Thomas Young taught us two
Hundred years ago, photons interfere.
But now we know that:
Knowledge of path (1 or 2) is the reason
why interference is lost. Its as if the photon
knows it is being watched.
But now we discover that:
Erasing the knowledge of photon path
brings interference back.
“No wonder Einstein was confused.”
Quantum Eraser: Mathematical Treatment
Do the case of Quantum Eraser similar to the Bertelsmann Socks ??
IS IT JUST DATA RECOVERY OR MANIPULATION??
Kim, Yu, Kulik, Shih, and Scully, PRL 84, 1 (2000)
Cavity QED based Quantum Eraser
Initial State:
1. Three-level ladder atom prepared
in the coherent superposition of
lower two-levels
2. A cavity Field prepared in the
superposition of zero and one
photon
3. Therefore the initial state comes to be;
Next we want to tag or entangled the atom with the cavity field.
Proposed Experimental Schematics
Tagging or entangling the atom with the cavity field.
M.S. Zubairy, G.S. Agarwal, M.O. Scully, Phys. Rev. A 70 (2004) 012316.
Delayed-Choice, Asymmetric Erasing
We note that the initial coherence of the atomic superposition
state and the related accessibility of the Ramsey interference pattern is
now lost due to its tagging or entanglement with the cavity field. To
recover back the Ramsey fringes, we need to erase the information carried
by the cavity field.
Distinguishability and Visibility: Englert–Greenberger–Yasin
duality relation
Delayed-choice adjustability for the path
distinguishability and fringe visibility
Strange and Mystifying: Fringe visibility/distinguishability can be
tuned in delayed-choice manner, even much later after the recording !!
M. Imran et al , Annals of Physics 364, 160 (2016).
Conclusions:
Time, information and the Quantum
The QUANTUM ERASER highlights all the
counterintuitive features of the quantum
theory and may serve as a test for any
interpretation of the theory whatsoever.
1. No experimental difference between real time
and delayed-choice. Concept of time is contrastly
different while dealing with classical and quantum
scenarios. Moreover, entropy of a pure quantum
state is always zero. So the arrow of time is
something of a mystery here. Our universe
appears to have a space-time structure in which
all of time is laid-out in a "block universe", i.e.,
there is no actual "flow" of time, no movement of
a "now" point.
2. In quantum theory, one must not talk of any result, e.g. which path
the quantum entity followed, in concrete terms unless an actual
measurement is performed. Similarly it also hints out that
state reduction should be better treated as a mental process
concerning information rather than a physical process.
3. Recently, a lot of work has been carried out suggesting the
ontological nature of the state vector or wavefunction. However, when
such a conjectured reality of the wavefunction is matched with the
DCQE results, it points out that the proposed reality of the
wavefunction is not ‘something existing out in the universe having
classical attributes’ and rather the state vector still carries
all the characteristics of the quantum theory including retrocausality
and the nonlocality. These ontological results therefore only marginally
rule out the Ψ-epistemic models and shed little further light on the
prominent foundational issues.
"If we attempt to attribute
an objective meaning to the
quantum state of a single
system, curious paradoxes
appear:
quantum
effects
mimic
not
only
instantaneous
action-at-adistance, but also, as seen
here, influence of future
actions on past events, even
after these events have been
irrevocably recorded."
Asher Peres
We note here: The present depends on the future but
there is no way the future can send a signal to the present !!
“How wonderful that we have met with a
paradox. Now we have some hope of making
progress.” Niels Bohr
Thanks and any Questions………