ResearchResearch Area B
Research propject B01

Project B01: Entangled neutral atoms for interferometry beyond the standard quantum limit

Within this project, we will employ spin-dependent collisional interaction in Bose-Einstein condensates to generate metrologically useful entanglement to overcome the standard quantum limit (SQL). In a new dedicated apparatus, a single-particle resolving detection scheme will allow to demonstrate a metrological sensitivity close to the Heisenberg limit for ensembles containing more than 100 atoms and a sensitivity of more than 20 dB below the SQL for up to 105 atoms. These states will be used to demonstrate the operation of a magnetometer and a frequency measurement beyond the SQL.

INTRODUCTION

Atom interferometers, which belong to today’s most precise sensors, are fundamentally limited by the standard quantum limit when operated with uncorrelated particles. Using entangled particles can overcome this limitation and the interferometer’s sensitivity is no longer limited by the SQL but by the Heisenberg limit. By employing spin-dependent collisional interaction in Bose-Einstein condensates, metrologically useful entanglement in atomic ensembles can be created.

In project A02, it has already been shown that entanglement in atom interferometers can be used to increase metrological sensitivity beyond the SQL. The achieved sensitivities were limited by the finite resolution in the atom number counting of ~15 atoms. Project B01 aims at combining the generation of entangled atomic many-particle states with a single-atom resolving detection scheme to demonstrate a Heisenberg-limited interferometric sensitivity.

RESULTS

Heisenberg-limited atom interferometry requires a specifically designed apparatus, which is being constructed within the first funding period. We have already implemented a new detection scheme using fluorescence imaging in a magneto-optical trap (MOT) to reach single-particle resolution. In contrast to absorption imaging, the signal-to-noise ratio is greatly enhanced due to the long lifetime of the MOT and the large signal of scattered photons. 

Single-particle resolution. The histogram shows the occurrences of the detected number of atoms in repeated counting experiments.

Up to now, a new dedicated apparatus consisting of a 3D MOT loaded by a 2D+ MOT is already set up. One of the main requirements, the single-particle resolving detection, has been demonstrated. The Figure above shows the current detection capabilities. On the x-axis, the number of counted fluorescence photons has been converted into an estimation of the measured number of atoms. The y-axis of the histogram records the number of occurrences in repeated counting experiments. The histogram shows clearly that the detection system discriminates between integer atom numbers with high fidelities for up to 20 atoms.   

Two-point variance and noise model extrapolation. Scattering rate noise (blue) is the dominant noise source compared to noise by atom loss (green), photon shot noise (yellow) and background noise (red). The inset shows the threshold at 390 atoms.

The second Figure shows the two-point variance for the data shown in the first Figure. The scattering rate noise (shown in blue) is the dominant noise contribution. The noise model can be used to extrapolate the atom counting performance towards higher atom numbers, reaching the accurate atom detection threshold for 390 atoms (see inset).

The single-particle resolving detection system allows to stabilize the number of atoms in a MOT with single-atom precision as shown in the Figure below (a). By introducing a controlled loss channel, the initial number of atoms can be reduced until the target atom number is reached. Similarly, the atom number in a magnetic trap can be stabilized by controlled RF loss pulses (b)

Atom number stabilization. (a) In a MOT, the atom number can be stabilized by switching off the repump light for short times until the target number of atoms is reached. (b) In a magnetic trap, by applying RF loss pulses.

FUTURE

The next step towards atom interferometry is the creation of Bose-Einstein condensates. The needed components and techniques are prepared and currently, we implement them into our experimental setup (figure 4). Allowing for spin-dependent collisional interaction in Bose-Einstein condensates creates metrologically useful entanglement. Combined with our single-particle resolving detection system, these are the key ingredients for a sensitivity beyond the SQL.

Our new apparatus will be used to demonstrate the operation of a magnetometer and a frequency measurement with Heisenberg-limited sensitivity.


PUBLICATIONS

  • Kristensen, M. A.; Christensen, M. B.; Gajdacz, M.; Iglicki, M.; Pawłowski, K.; Klempt, C.; Sherson, J. F.; Rzążewski, K.; Hilliard, A. J.; Arlt, J. J. (2019): Observation of Atom Number Fluctuations in a Bose-Einstein CondensatePhys. Rev. Lett. 122, 163601
    DOI: 10.1103/PhysRevLett.122.163601
  • Kristensen M., Gajdacz M., Pedersen P., Klempt C., Sherson J.F., Arlt J.J., Hilliard A.J. (2017): Sub-atom shot noise Faraday imaging of ultracold atom cloudsJ. Phys. B: At. Mol. Opt. Phys. 50 034004
    DOI: 10.1088/1361-6455/50/3/034004
  • Gajdacz M., Hilliard A.J., Kristensen M.A., Pedersen P.L., Klempt C., Arlt J.J., Sherson J.F. (2016): Preparation of ultracold atom clouds at the shot noise levelPhys. Rev. Lett. 117, 073604
    DOI: 10.1103/PhysRevLett.117.073604
All publications of the Collaborative Research Centre

PROJECT LEADER

apl. Prof. Dr. Carsten Klempt
Address
Welfengarten 1
30167 Hannover
Building
Room
Address
Welfengarten 1
30167 Hannover
Building
Room
Prof. Dr. Luis Santos
Address
Appelstraße 2
30167 Hannover
Building
Room
249
Address
Appelstraße 2
30167 Hannover
Building
Room
249
Prof. Dr. Wolfgang Ertmer
Address
Welfengarten 1
30167 Hannover
Building
Room
Address
Welfengarten 1
30167 Hannover
Building
Room

STAFF

Dr. Jiao Geng
Address
Welfengarten 1
30167 Hannover
Dr. Jiao Geng
Address
Welfengarten 1
30167 Hannover
Mareike Hetzel
Address
Welfengarten 1
30167 Hannover
Mareike Hetzel
Address
Welfengarten 1
30167 Hannover
Cebrail Pür
Address
Welfengarten 1
30167 Hannover
Cebrail Pür
Address
Welfengarten 1
30167 Hannover