• ABSTRACT – BELL TEST IN SUPERCONDUCTING SYSTEMS

We perform our Bell test on two qubits (quantum bits) of a small superconducting quantum computer comprising four quantum bits. The entire setup is controlled by custom software, which is waiting for being fed with random numbers to execute the various instances of the Bell test according to the free will of volunteers. Qubits – unlike classical bits – can represent any superposition between 0 and 1. In our case they are encoded in a combination of charges that are allowed to coherently jump between two pieces of superconducting aluminum. For the processor to work it is cooled to a temperature of 25 mK (100 times cooler than outer space!). This cool temperature not only renders the entire chip superconducting, but also suppresses electrical noise to an extent that makes it possible to precisely control the states of the qubits using microwave radiation (the same kind as the one used in a microwave oven or in WiFi). The radiation is guided in cables, similar to optical fibers, from generators and modulators into the special refrigerator in which the quantum processor is mounted.

• FACTS
  • The Bell test in Zurich is done by 5 quantum logic operations on small quantum computer.
  • and with a small superconductive quantum computer.
  • and runs on a processor 100 time cooler than outer space.
  • and is measured 10 000 times every second.
  • and is cooled by liquid Helium and quantum effects.
  • and makes uses microwave photons instead of visible light.

• QUOTE

“This experiment is quite different from our daily life in the laboratory as we usually do not have really fixed deadlines. In experimental science the problems always appear when least expected. This time we were not able to postpone the final experiments and to get all of the problems solved in time we really felt the importance of working as a good team we are.”

1. Name of lab:

Quantum Device Lab

2. Team:

Kraglund Andersen, Adrian Beckert, Christopher Eichler, Johannes Heinsoo, Sebastian Krinner, Philipp Kurpiers, Paul Magnard, Markus Oppliger, Yves Salathé, Theodore Walter, Andreas Wallraff (PI).

3. Organization:

ETH Zurich

4. City:

Zurich

5. GPS coordinates of the experiment:

Latitude: 47.409822, Longitude: 8.509535

6. Name of the experiment:

BBT with superconducting qubits

7. Target Bell inequality and experimental result obtained:

CHSH (Clauser-Horne-Shimony-Holt) inequality: local realism implies |S|≤2.  We obtained a value for S of 2.3066 ± 0.0012 with a p-value less than 10^(-99).

8. What did the experiment test?

If CHSH Bell inequality is still violated if measurement bases are chosen by humans.

9. Physical system used:

Superconducting transmon qubits.

10. Degree of freedom measured:

Two lowest lying energy eigenstates of the transmon artificial atom.

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

On average we used 107 bps. In total about 19 Mb.

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

Depending on the random bits a different set of microwave pulses was applied to the qubits.

13. How long did the experiment take?

48.9 hours, from 12.38 to 13.37 of November 30, CET.

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

We stored the retrieved bits on a hard disk and immediately used them in the experiment on a timescale from 10 seconds to 2 hours after receiving them.

15. Distance between Alice and Bob:

2 mm.