1. Presented By: Muhammad Imran PhD student (PIEAS)
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.

2. The seminar is based upon our recently published work
Layout of the Talk
Introduction to Delayed Choice Experiment (DCE)
QDCE in Bragg Regime Cavity QED
Setup and Results
Conclusions

3. Wheeler’s Delayed Choice & Double Slits Experiment

4. 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.
or (b) measure at plane s2 which indicating that it has passed only through slit 2. * * *
The observer waits until after the photon has passed the slits to decide which measurement to do.

5. Wheeler’s Delayed Choice & Mach-Zehnder interferometer

6. Wheeler delayed choice experiment
Wheeler: The photon took the upper path

7. 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

8. Wheeler delayed choice experiment
Wheeler: The photon took both paths
Otherwise, the interference cannot be explained

9. 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
If BS2 is present we observe interference fringes, indicating the photon behaved as a wave, traveling both arms of the MZI.
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.

10. 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.

11. 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.

12. Wave-particle complementarity
Wave-particle complementarity is given by a Mach-Zehnder 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 beam-splitter BS2 before detection. [Ref.*].
[Ref.*] Radu Ionicioiu and Daniel R. Terno, Proposal for a Quantum Delayed-Choice Experiment, Phys. Rev. Lett. 107, (2011).

13. 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, , (2015)

14. 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, , (2015)

15. 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,

16. 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,

17. 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

18. 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.

19. QDCE, Result

20. Conclusion
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.
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.
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.

21. Questions
Any Question