• ABSTRACT – ENTANGLEMENT THROUGH TIME!

Our experiment will study quantum correlations in time. Quantum entanglement is usually thought of as a strong connection between two (or more) particles that are separated in space. Such entanglement can be revealed by Alice and Bob, who each measure one of these particles, in a Bell-inequality test. However, quantum correlations cannot only exist across space. Alice and Bob could also be separated in time, rather than space, and perform their measurements on the same quantum system at different times. Such an experiment can reveal so-called temporal entanglement, which is a much less well-known form of entanglement. In our experiment Alice and Bob will use human-generated random numbers to choose measurement settings for a Bell-inequality test for temporal quantum correlations. Studying temporal quantum correlations will help us to understand the structure and power of quantum correlations. 

• FACTS
  • Quantum entanglement is the strongest link between two particles that exists in nature. Yet, it is not the strongest allowed by the laws of physics. Why quantum entanglement is just as strong as it is and not stronger is still an open question.
  • For a weekend during Brisbane summer the Quantum Technology Lab was run by a family of brushtail possums.
  • Bell”s theorem shows that quantum particles do not follow the rules of cause and effect as we know it.
  • When two quantum particles are entangled, they behave as if they were one. No matter how far apart they are in space, or time.
  • Quantum entanglement is across space is exclusive. If Alice is entangled with Bob, then Bob cannot, at the same time, be entangled with Charlie.
  • When you are sitting still, you are actually traveling through time, and according to quantum mechanics, your present self can be entangled with your past, or future self.
  • Quantum correlations cannot be explained as cause and effect, even if Alice”s measurement outcome influences Bob”s at infinite speed.

 

• QUOTE

“Thanks to all the Bellsters who provided de random numbers we needed to keep our experiments going!”

1. Name of lab:

Quantum Technology Lab

2. Team:

Martin Ringbauer, Tara Roberson, and Andrew White (PI).

3. Organization:

EQuS – ARC Center of Excellence for Engineered Quantum Systems, University of Queensland

4. City:

Brisbane

5. GPS coordinates of the experiment:

27°29″53.9″S, 153°00″47″E

6. Name of the experiment:

Quantum Entanglement in Time

7. Target Bell inequality and experimental result obtained:

CHSH (Clauser-Horne-Shimony-Holt) inequality in time as in Brukner et al. between three observers, Alice, Bob and Charlie, who perform sequential measurements on a single quantum system. We find that the temporal CHSH inequality can simultaneously be violated between Alice and Bob, and between Bob and Charlie.Both CHSH inequalities (between Alice and Bob, and between Bob and Charlie) were violated by more than 15 standard deviations. This demonstrates that a key property of entanglement in space, so-called monogamy of entanglement, does not hold in the temporal domain.

8. What did the experiment test?

Our experiment tested quantum entanglement in time on a single quantum system. We tested entanglement between two observers separated in time, as well as the role of entanglement monogamy between three observers in the temporal domain.

9. Physical system used:

Photons.

10. Degree of freedom measured:

Polarization.

11. Rate of bits consumed & total number of bits:

Our experiment consumed a total of 6300 bits to determine the measurement settings of Alice, Bob, and Charlie. In the final data collection, we recorded an average of about 1.5 events per outcome for each setting choice.

12. What was the use of the bits of the Bellsters?

The bits we received from the Bellsters were used to set the angle of motorized waveplates. These waveplates are used to rotate the polarization of our photons, which allows Alice, Bob, and Charlie to measure their photons in different directions for our Bell test.

13. How long did the experiment take?

The experiment was broken up into 7 segments of roughly 8 hours each. The first run started on Nov. 29, 22:19:30 local time, and the last measurements started on Dec 1, 20:53:06 local time.

14. Did you use all the bits in real time?

Since our experiment tested quantum entanglement in time, the important feature was that the bits were random and uncorrelated, rather than that they are delivered in real time. We thus used the unique human-generated randomness of the bits we received to program a sequence of measurements for Alice, Bob, and Charlie into our experiment, split into 7 independent runs of 8 hours each.

15. Distance between Alice and Bob:

For our experiment the distance between Alice, Bob, and Charlie did not matter. We were interested in a situation where they are separated in time, such that Alice is before Bob, who is before Charlie. The separation in time was about 2/3 of a nanosecond between each observer.