• ABSTRACT: MEASURING CORRELATIONS WITH THE HELP OF HUMANS

Our light source produces photon pairs with high correlation in their polarizations. Each photon of the pair is sent in different directions, towards two similar detection stages. Upon arrival to the detection stages, they travel through a waveplate that defines an orientation for polarization measurement, and a polarizer that projects the photon into two orthogonal polarization states. Naming the two possible outcomes (+) and (-) on each stage, the experiment consists in counting correlations between the possible outcomes of the whole experiment; (++), (+-), (-+) and (–); and compare the results with correlation limits imposed by different theories. 

• FACTS
  • At the Buenos Aires laboratory, all the Waveplates and phase plates required to manipulate polarization and path quantum states are motorized. Some of them are mounted on stepper motors, and others are actuated with Arduino-controlled servo motors.
  • The experimental setup at the Buenos Aires laboratory was originally used to implement quantum teleportation of a quantum bit between two separated stages, roughly four meters away from each other.
  • Photons that propagate in open air at the Buenos Aires experiment are spatially filtered by coupling light with single mode fibers before the detection.
  • In order to detect coincidences between photons at the two sides of the experiment, electrical cables must compensate different optical delays on the photon paths with a precision of 5E-10s (10 cm of cable).

 

• QUOTE

“The team at Buenos Aires; Laura, Nacho, Agus, Chris, Ari and Richi want to say THANK YOU BELLSTERS!!!The “B”-day started early at Buenos Aires!! We didn’t want to miss the fun due to the time difference with Barcelona. For us it was the first time that ALL the Lab crew was simultaneously involved in a single experiment. Big Bell Test = Big Time Fun.”

1. Name of lab:

División Óptica Cuántica, DEILAP (CITEDEF-CONICET)

2. Team:

Laura T. Knoll, Ignacio H. López Grande, Agustina G. Magnoni, Christian T. Schmiegelow,Ariel Bendersky, and Miguel A. Larotonda.

3. Organizations:

DEILAP (CITEDEF-CONICET)andDepartamento de Física, FCEyN, Universidad de Buenos Aires

4. City:

Villa Martelli, Buenos Aires

5. GPS coordinates of the experiment:

34°33″19.9″S 58°30″22.8″W

6. Name of the experiment:

Violation of the CHSH inequality using polarization-entangled photons.

7. Targeted Bell inequality and experimental results obtained.

The experiment tested the S-value of the CHSH (Clauser-Horne-Shimony-Holt) inequality: local realism implies |S|≤2. We obtained a value for S of 2.55 ± 0.07, which corresponds to a violation of the inequality by more than 7.8 standard deviations.

8. What did the experiment test?

The experiment tested the existence of non-classical correlations of a particular degree of freedom (in this case the photon’s polarization) between two particles of a single composite system. These correlations arise as a consequence of one of the most distinguishing features of quantum mechanics, which is the entanglement.

9. Physical system used:

In our case the physical system is a photon pair created from a single input photon by means of a nonlinear optical process known as Spontaneous Parametric Downconversion.

10. Degree of freedom measured:

Photon polarization.

11. Rate of bits consumed & total number of bits

The overall bitrate was 1.02bps (bits per second) totalling 33920 bits during the whole experiment.

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

Random bits retrieved from the server were used to rotate two half-waveplates, located at Alice and Bob’s setups. Waveplates are optical elements whose orientation angle rotates the polarization axis of the incoming photon. This action, combined with a static polarizing beam divider placed afterwards, acted as a projector of the polarization, i.e., a choice of the measurement basis for polarization. The waveplates were rotated with motorized actuators that used stepper motors drived by software.

13. How long did the experiment took?

The data gathering for the experiment took nine hours, starting an 9:00 AM November 30, and ending at 6:00 PM (BA time).

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

Since our bit usage rate was on the order of 0.5Hz, the bits were buffered by hundreds every 10 minutes. In this way we made sure that we used bits generated by the Bellsters throughout the whole BBT day.

15. Distance between Alice and Bob:

The distance between Alice and Bob setups was approximately 3.5 meters.