Download The Transactional Interpretation of Quantum Mechanics http://www

Wheeler’s Delayed Choice
in
Bragg Regime Cavity QED
Presented By:
Muhammad Imran
PhD student (PIEAS)
National Institute of Lasers and Optronics, (NILOP) Islamabad.
Pakistan Institute of Engineering and Applied Sciences,
Nilore, Islamabad, Pakistan.
The seminar is based upon our recently published work
Layout of the Talk
1. Introduction to Delayed Choice Experiment (DCE)
2. QDCE in Bragg Regime Cavity QED
3. Setup and Results
4. Conclusions
Wheeler’s Delayed Choice
&
Double Slits Experiment
Wheeler’s Delayed Choice
The “past” and the “Delayed Choice” Double-Slit Experiment
J.A. Wheeler 1978
A source emits one photon.
Its wave function passes
through slits 1 and 2, making
*
interference beyond the slits.
*
The observer can choose to either:
(a) measure the interference pattern
at plane s1, requiring that the
photon travels through both slits. The observer waits
until after the photon
or
has passed the slits to
(b) measure at plane s2 which
indicating that it has passed only decide which
measurement to do.
through slit 2.
Wheeler’s Delayed Choice
&
Mach-Zehnder interferometer
Wheeler delayed choice experiment
Wheeler: The photon took the upper path
Wheeler delayed choice experiment
Wheeler: The photon took the upper path
It could not come the other way
The trace shows Wheeler’s past of the photon
Wheeler delayed choice experiment
Wheeler: The photon took both paths
Otherwise, the interference cannot be explained
In the classical delayed-choice experiment the
second beam-splitter is inserted or removed
randomly after the photon is already inside the
interferometer.
Two Possibilities
1. If BS2 is present we observe interference
fringes, indicating the photon behaved as a
wave, traveling both arms of the MZI.
2. If BS2 is absent, we randomly register, with
probability 1/2 , a click in only one of the two
detectors, concluding that the photon
travelled along a single arm, showing particle
properties.



One randomly chooses whether or not
to insert the second beam splitter when
the photon is already inside the
interferometer and before it reaches
BS2.
The photon should not “know”
beforehand if it has to behave like a
particle or like a wave.
The choice of inserting or removing BS2
is classically controlled by a random
number generator.
Bohr’s complementarity principle:

The wave and particle characters of
light are complementary;

If a measurement (experimental
setup) proves the wave character of
matter, Then it is impossible to
prove the particle character in the
same measurement and conversely.
Wave-particle complementarity
Wave-particle complementarity is given by a MachZehnder interferometer (MZI). A photon is first split
by beam-splitter BS1, travels inside an
interferometer with a tunable phase shifter ᶲ and is
finally recombined (or not) at a second beamsplitter BS2 before detection. [Ref.*].
[Ref.*] Radu Ionicioiu and Daniel R. Terno, Proposal for a Quantum Delayed-Choice Experiment,
Phys. Rev. Lett. 107, 230406 (2011).
Quantum Delayed-Choice Experiment
in Bragg Regime Cavity QED
we propose a matter-wave Mach-Zehnder-Bragg
cavity-QED interferometric setup with final QBS
engineered through a cavity field that is taken
initially in the superposition of zero and one photon.
[Ref.**].
[Ref.**] Manzoor Ikram, Muhammad Imran, Tasawar Abbas and Rameez-ul- Islam. “Wheeler's delayed-choice
experiment: A proposal for the Bragg-regime cavity-QED implementation” Phys. Rev. A 91, 043636, (2015)
QDCE: Mach-Zehnder-Bragg
Interferometric Implementation
Proposed Mach-Zendher-Bragg cavity-QED interferometric experimental setup.
[Ref.**] Manzoor Ikram, Muhammad Imran, Tasawar Abbas and Rameez-ul- Islam. “Wheeler's delayed-choice
experiment: A proposal for the Bragg-regime cavity-QED implementation” Phys. Rev. A 91, 043636, (2015)
The high-Q cavities C1 and (C2,C3) contain Fock
fields (nc ) and (mc) acting as atomic de Broglie
beam splitter (AdB-BS) and atomic de Broglie
mirrors (AdBM), respectively.
However, the fourth cavity, i.e., C4, that
acts as the final quantum beam splitter, QAdB-BS,
is initially prepared in the superposition state:
1. We consider a two-level atom, The initial
state of the atom-field system,
2. After interaction with the cavity C1 forming the
first AdB-BS of the Mach- Zehnder interferometer,
gets transformed,
3. Next, this state passes through the two AdB-M
mirror cavities C2 and C3, gets transformed,
4. Now, this two-level atom bearing both particle
and wave attributes, and in superposition of its
external transverse momenta states, faces the
final beam splitter QAdB-BS2 which is a quantum
beam splitter initially in state,
Now the initial composite state of the atom-field
system for the final interaction
 This suggests that when the Bragg-diffracted
atom faces vacuum-state cavity |0c > (the
absence of AdB-BS2) gives the particle
signatures,
 And when cavity (C4) having a |1c > field state
(presence of the quantum beam splitter)
resulting in interference fringes. Thus the atom in
this case will exhibit its wave nature while
suppressing the particle signatures.
QDCE, Result
Conclusion
1. we have a quantum beam-splitter in superposition
of being present or absent, the interferometer is in
a superposition of being closed or open. This
forces the quantum entity to be in a superposition
of particle and wave at the same time.
2. The proposal, explicitly elaborates that both
particle and wave aspects can be handled in a
single QDCE experimental arrangement in striking
contrast with Bohr’s point of view.
3. Our proposal explicitly exhibits the particle and
wave aspects of the actual matter waves and
hence highlights the modification of the
complementarity concept in its true sense.
Questions
21