Can superdense coding be achieved without quantum memory?

  • Context: Undergrad 
  • Thread starter Thread starter Armchair
  • Start date Start date
  • Tags Tags
    Coding Memory
Click For Summary
SUMMARY

The discussion centers on the feasibility of achieving superdense coding without quantum memory, as explored in the paper by Julio T. Barreiro and Paul G. Kwiat. The authors propose that superdense coding can be performed using hyperentangled photon pairs, allowing the transmission of two classical bits per qubit through polarization and spatial mode entanglement. However, the process involves significant control requirements and post-selection steps, which may undermine claims of increased communication capacity. The consensus is that while superdense coding is theoretically possible in this framework, practical limitations exist.

PREREQUISITES
  • Understanding of superdense coding principles
  • Familiarity with hyperentangled photon pairs
  • Knowledge of quantum measurement and entanglement
  • Basic concepts of quantum communication protocols
NEXT STEPS
  • Research the principles of superdense coding in quantum information theory
  • Explore the role of hyperentanglement in quantum communication
  • Study quantum measurement techniques and their impact on entanglement
  • Investigate the implications of post-selection in quantum experiments
USEFUL FOR

Quantum physicists, researchers in quantum communication, and anyone interested in the practical applications and limitations of superdense coding techniques.

Armchair
Messages
5
Reaction score
0
In superdense coding how can BSA be performed on the second of a pair of hyperentangled photons if the photon that was sent sometime earlier was measured on arrival? Would not the measurement have destroyed the entanglement?
I’m trying to understand superdense coding as set out in this paper.
It is suggested here that quantum memory is not required.

Hyperentanglement for advanced quantum communication
Julio T. Barreiro and Paul G. Kwiat
Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801-3080,
USA
 
Physics news on Phys.org
For some reason, this paper thinks that "superdense coding" means sending two classical bits of information with a single photon. It actually means sending two classical bits per qubit. Since the experimenters can put two qubits into their photons (one for polarization, one for spatial mode), they would actually have to send four bits of information per photon to be properly superdense coding.

The experiment they describe is:

1. A polarization-and-spatial-mode-entangled photon pair is generated with one part sent to Alice and the other part to Bob.
2. Alice uses her part to do a measurement with a desired preparation as one of the results.
3. If the measurement returns the wrong answer, give up and try again.
4. If the measurement gave the right answer, Bob's photon was prepared into a state where its polarization is entangled with its spatial mode.
5. Bob encodes two bits into the photon. Bob only operates on the polarization of the photon, which would normally limit him to encoding one bit, but the entanglement with the spatial mode allows for 2. This is the only sense in which superdense coding is used.
6. Bob sends the photon to Alice, who decodes it.

In other words: instead of using superdense coding to increase bandwidth, they're using it to decrease control requirements.

Also, I personally find it silly to claim anything related to increased communication capacity when performing steps that require post-selection (step 3). If they're preparing two qubit states, then the retry rate is probably 75% and any bandwidth-per-photon that they report probably needs to be divided by 4.
 

Similar threads

Undergrad Human eyes can detect single photons?
  • · Replies 19 ·
Replies
19
Views
3K