• ABSTRACT Experiment 1 – ENTANGLEMENT BEWTEEN ATOMS AND LIGHT: QUANTUM MEMORIES FOR QUANTUM INFO!

Our experiment will test the Bell correlations between two very different quantum objects: a single photon and a single collective spin-excitation (called a spin-wave) involving millions of atoms in a laser-cooled atomic cloud. We will generate entanglement probabilistically between a photonic time-bin qubit well suited for transmission in optical fibers and a spin-wave qubit stored in a quantum memory. After a controllable storage time, the spin-wave qubit will be converted deterministically into another photonic time-bin qubit. Both photonic qubits were analysed using optical interferometers. The random numbers provided by the public will be used to randomly choose the measurement bases by changing the phase of each interferometer using a piezoelectric device.

• ABSTRACT Experiment 2 – FREQUENCY-BIN ENTANGLEMENT

We test the two-photon interference in frequency between a visible photon and its partner at telecom wavelengths.  We check correlations and coherent superposition of frequency modes in the photon spectrum. Due to the generation process the photons are created in a superposition of multiple spectral modes. Due to energy conservation, two photons generated at the same time as a pair in the parametric down conversion process are correlated in their frequency. Due to the multimode shape of the spectrum we can identify each spectral mode as a discrete frequency-bin. We use this fact and test the Bell inequality in the time-frequency degree of freedom. The random bits sent by the Bellsters controlled the phase and amplitude of the radio-frequency signal driving two modulators whose purpose was to generate a superposition of the spectral modes.

• FACTS
  • We generate entanglement between two very different quantum objects: a single photon and a cloud of 1 million Rubidium atoms.
  • Our experiment involves 1 million Rubidium atoms cooled to 100 micro degrees above absolute zero (around -273 degrees Celsius) inside an ultra-high vacuum chamber, with a pressure 1 trillion time smaller than atmospheric pressure. And it works!
  • The atoms in our vacuum chamber move at a velocity of 10 cm per second, about 5000 times slower than the molecules of air at room temperature.
  • To analyze our entangled state, we need to stabilize the length of a 40 meters long optical fiber with a precision of less than 50 nanometers.
  • The entanglement can be stored for a programmable time in our cloud of cold atoms, which serves as a quantum memory.

• QUOTE

“It was an amazing experience. It was great to see random numbers from people all around the world take control of our experiment. Thanks to the Bellsters!”

1. Name of lab:

Quantum Photonics With Solids And Atoms

2. Team:

Experiment 1: Georg Heinze, Pau Farrera, and Hugues de Riedmatten (PI). Experimental results comming soon.Experiment 2: Andreas Lenhard, Alessandro Seri, Daniel Rieländer, Osvaldo Jimenez, Alejandro Máttar, Daniel Cavalcanti, Margherita Mazzera, Antonio Acín, and Hugues de Riedmatten (PI).

3. Organization:

ICFO – Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology

4. City:

Castelldefels, Barcelona

5. GPS coordinates of the experiment:

6.41°16″28.7″N 1°59″21.1″E

6. Name of the experiment:

ICFO Experiment 2 – Frequency-Bin Entanglement

7. Target Bell inequality and experimental result obtained

CHSH (Clauser-Horne-Shimony-Holt) inequality: local realism implies |S|≤2. The result of the Bell test was S = 2.25 ± 0.08. This is a violation by more than 3 standard deviations.Other measurements have been done at a later stage with stored human random numbers, leading to a much stronger violation.

8. What did the experiment test?

In the experiment we test the two-photon interference between a photon at visible and its partner at telecom wavelengths in the frequency degree of freedom. We check correlations and coherent superposition of frequency modes in the photon spectrum. Due to the multimodality of the spectrum we demonstrate the high-dimensional entanglement of frequency-bins of the photons.

9. Physical system used:

We use photons generated via cavity enhanced spontaneous parametric down conversion (SPDC). One of the photons is at visible wavelengths while its partner is at a telecom wavelength. Due to the generation process the photons are created in a superposition of multiple spectral modes.

10. Degree of freedom measured:

Due to energy conservation, two photons generated at the same time as a pair in the parametric down conversion process are correlated in their frequency. Due to the multimode shape of the spectrum we can identify each spectral mode as a discrete frequency-bin. We use this fact and test the Bell inequality in the time-frequency degree of freedom.

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

The sequence was asking for 16 bits of random numbers every 10s of measurement time.For the long measurement run we consumed 87152 bits in 19.7 hours.Time tags Start: 1480617676586; Stop 1480685757478

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

The bits controlled the phase and amplitude of the radio-frequency signal driving two modulators in the setup. The purpose of these modulator is to mix the spectral components of the photons and add a phase to them. We have two electro-optic modulators (EOM) in our setup. These generate a superposition of the spectral modes including a phase. The random bits set the phase and the amplitude of the radio-frequency signals sent to these modulators.

13. How long did the experiment take?

Our first measurement controlled by the Bellsters started on 29/11/16 at 21:00 and lasted for 93 minutes. We continued measuring and finished with the help of Bellsters at 02/12/16 at 15:23h. The longest measurement was running almost 20 hours including the night from 01/12 to 02/12.

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

We divided our measurement in trials of 10s duration. At the beginning of each such sequence we collected fresh numbers from the Bellsters and changed the settings of the experiment according to the numbers. Then we collected photon detection events for 10s. Afterwards we ask for fresh numbers, and so on.

15. Distance between Alice and Bob:

The distance is less than 1m the whole experiment is setup on one optical table.