Bjorn Lauritzen

Telecommunication-wavelength solid-state memory at the single photon level.

We demonstrate experimentally the storage and retrieval of weak coherent light fields at telecommunication wavelengths in a solid. Light pulses at the single photon level are stored for a time up to 600 ns in an erbium-doped Y2SiO5 crystal at 2.6 K and retrieved on demand. The memory is based on photon echoes with controlled reversible inhomogeneous broadening, which is realized here for the first time at the single photon level. This is implemented with an external field gradient using the linear Stark effect. This experiment demonstrates the feasibility of a solid-state quantum memory for single photons at telecommunication wavelengths, which would represent an important resource in quantum information science.

Towards an efficient atomic frequency comb quantum memory

We present an efficient photon-echo experiment based on atomic frequency combs [Phys. Rev. A 79 (2009) 052329]. Echoes containing an energy of up to 35% of that of the input pulse are observed in a Pr3+ -doped Y2SiO5 crystal. This material allows for the precise spectral holeburning needed to make a sharp and highly absorbing comb structure. We compare our results with a simple theoretical model with satisfactory agreement. Our results show that atomic frequency combs has the potential for high-efficiency storage of single photons as required in future long-distance communication based on quantum repeaters. (c) 2010 Elsevier B.V. All rights reserved.

Atomic frequency comb memory with spin-wave storage in 153Eu3 +:Y2SiO5

153Eu3 +:Y2SiO5 is a very attractive candidate for a long-lived, multimode quantum memory due to the long spin coherence time (?15 ms), the relatively large hyperfine splitting (100 MHz) and the narrow optical homogeneous linewidth (?100 Hz). Here we show an atomic frequency comb memory with spin-wave storage in a promising material 153Eu3 +:Y2SiO5, reaching storage times slightly beyond 10 ?s. We analyse the efficiency of the storage process and discuss ways of improving it. We also measure the inhomogeneous spin linewidth of 153Eu3 +:Y2SiO5, which we find to be 69 ? 3 kHz. These results represent a further step towards realizing a long-lived, multimode solid-state quantum memory.

State preparation by optical pumping in erbium-doped solids using stimulated emission and spin mixing

Erbium-doped solids are potential candidates for the realization of a quantum memory for photons at telecommunication wavelengths. The implementation of quantum memory proposals in rare-earth-ion-doped solids require spectral tailoring of the inhomogeneous absorption profile by efficient population transfer between ground-state levels (spin polarization) using optical pumping. In this paper we investigate the limiting factors of efficient optical pumping between ground-state Zeeman levels in an erbium-doped Y2SiO5 crystal. We introduce two methods to overcome these limiting factors: stimulated emission using a second laser and spin mixing using radio frequency excitation. Both methods significantly improve the degree of spin polarization. Population transfer between two Zeeman levels with less than 10% of the total population in the initial ground state is achieved, corresponding to a spin polarization greater than 90%. In addition, we demonstrate spectral tailoring by isolating a narrow absorption peak within a large transparency window.

Electric control of collective atomic coherence in an erbium-doped solid

We demonstrate the fast and accurate control of the evolution of collective atomic coherences in an erbium-doped solid using external electric fields. This is achieved by controlling the inhomogeneous broadening of erbium ions emitting at 1536 nm using an electric field gradient, thanks to the linear Stark effect. The manipulation of atomic coherence is characterized with the collective spontaneous emission (optical free induction decay (FID)) emitted by the sample after an optical excitation, which does not require any previous preparation of the atoms. We show that controlled dephasing and rephasing of the atoms by the electric field result in collapses and revivals of the optical FID. Our results show that the use of external electric fields does not introduce any substantial decoherence and enables the manipulation of collective atomic coherence with a very high degree of precision on the timescale of tens of nanoseconds. This provides an interesting resource for photonic quantum state storage and quantum state manipulation.

Solid state quantum memories for quantum repeaters

Quantum memories are necessary for the implementation of quantum networks and repeaters. Recent progress towards photonic quantum storage in solid state atomic ensembles using photon echo techniques will be presented.

Towards Multimode Memories with Atomic Ensembles in the Solid State

Atomic ensembles in the solid state using rare-earth ion doped materials can be used to implement a quantum memory for the storage of multiple temporal modes. First experimental steps will be presented.