Research Activities

Our research focuses on the coherent control of matter and light [1]. A.K. was first to demonstrate single-photon sources based on atom-photon coupling in optical cavities [2], and extended these to quantum interfaces for entangling atoms and photons [3,4]. We now design novel schemes to fully control the atom-photon coupling in cavities [5,6]. This does encompass single-photon quantum memories [7] and quantum state mapping in connection with the fully deterministic shaping of photon amplitudes and phases in space and time [8]. Furthermore, we develop methods for trapping and cooling large arrays of individual atoms in cavities using optical tweezers [9], which will pave the way to large-scale quantum processing networks.

  1. A. Kuhn and D. Ljunggren. Contemporary Physics, 51:289, 2010.
  2. A. Kuhn, M. Hennrich, and G. Rempe. Phys. Rev. Lett., 89:067901, 2002.
  3. T. Wilk, S. C. Webster, A. Kuhn, and G. Rempe. Science, 317:488, 2007
  4. M. Hijlkema, B. Weber, H. P. Specht, S. C. Webster, A. Kuhn, and G. Rempe. Nature Physics, 3:253, 2007
  5. G. S. Vasilev, D. Ljunggren, and A. Kuhn. New Journal of Physics, 12 (6):063024, 2010
  6. J. Dilley, P. Nisbet, B. W. Shore, and A. Kuhn. arXiv:1105.1699v1 [quant-ph], 2011
  7. M. Himsworth, P. Nisbet, J. Dilley, G. Langfahl-Klabes, and A. Kuhn. Appl. Phys. B, 103:579-589, 2011
  8. P. Nisbet, J. Dilley, and A. Kuhn. arXiv:1106.6292v1 [quant-ph], 2011
  9. L. Brandt, C. Muldoon, T. Thiele, J. Dong, E. Brainis, and A. Kuhn. Appl. Phys. B, 102:443-450, 2011

Optical trapping and manipulation of single atoms

Atoms in optical tweezers: Optical trapping and manipulation in arbitrary potentials
We have realised a dipole-trapping scheme for arbitrarily manipulating, addressing and positioning of individual atoms in two dimensions. To this purpose, we use the image of a micro-mechanical mirror array to form a two-dimensional array of individual dipole traps. The micro mirrors are very versatile and fast, which allows an in-situ rearrangement of trapped atoms to any arbitrary pattern, under the permanent control through a confocal microscope.

The individual mirrors can be switched between two positions, so that the reflected light is either directed onto the trapped atoms, or misses the microscope lens and hits a beam stop. With a mirror placed underneath the image plane, a standing-wave dipole trap will be formed that allows one to hold individual atoms. Switching groups of mirrors in an appropriate fashion enables one to move atoms to different places without loosing them.

Single photon shaping and storage

Arbitrary shaping of single photons
Isolated single atoms are coupled to a high-finesse optical cavity and are exposed to classical laser pulses in a way that they can be used to emit or absorb single photons in a controlled manner. These kind of atom-cavity systems are highly suited for the use as a deterministic single-photon source for the generation of narrowband single-photon pulses.

The photons are emitted on demand into a well-defined mode of the radiation field. They are generated by an adiabatically driven Raman transition, with the vacuum field of the cavity stimulating one branch of the transition, and laser pulses driving the other. Antibunching is found in the intensity correlation of the light, demonstrating that a single atom emits photons one-by-one. The photons have properties close to laser light - they propagate into one direction, they all have the same frequency and cannot be distinguished from one another. This particular feature makes these photons well suitable for quantum information processing.

Storage and retrieval of single photons using EIT

For quantum networking, an essential feature is the mapping of single-photon states onto atomic quantum states and vice versa, i.e. the storage and retrieval of a photonic qubit by one or many atoms. To this purpose, narrowband single photons are required, which are in resonance with the relevant atomic transition. We intend to slow down and stop a single photon in atomic vapour, using the well-known effect of electromagnetically induced transparency (EIT). A reversal of the storage process leads to a re-emission of the photon. Many-photon interferences (Hong-Ou-Mandel correlations) will be used to characterise that the restored photon is equivalent to the one which was originally stored in the vapour. This way of storage and retrieval of individual photons in atomic vapour will allow one to realise quantum memories and arbitrary delay lines in quantum networks.