arXiv subjects

Mikael Afzelius

Publications and source records attributed to Mikael Afzelius.

66 records · Page 4Linked to original sources

arXiv2010

On the impossibility of faithfully storing single-photons with the three-pulse photon echo

The three-pulse photon echo is a well-known technique to store intense light pulses in an inhomogeneously broadened atomic ensemble. This protocol is attractive because it is relatively simple and it is well suited for the storage of multiple temporal modes. Furthermore, it offers very long storage times, greater than the phase relaxation time. Here, we consider the three-pulse photon echo in both two- and three-level systems as a potential technique for the storage of light at the single-photon level. By explicit calculations, we show that the ratio between the echo signal corresponding to a single-photon input and the noise is smaller than one. This severely limits the achievable fidelity of the quantum state storage, making the three-pulse photon echo unsuitable for single-photon quantum memory.

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arXiv2010

Mapping multiple photonic qubits into and out of one solid-state atomic ensemble

The future challenge of quantum communication are scalable quantum networks, which require coherent and reversible mapping of photonic qubits onto stationary atomic systems (quantum memories). A crucial requirement for realistic networks is the ability to efficiently store multiple qubits in one quantum memory. Here we demonstrate coherent and reversible mapping of 64 optical modes at the single photon level in the time domain onto one solid-state ensemble of rare-earth ions. Our light-matter interface is based on a high-bandwidth (100 MHz) atomic frequency comb, with a pre-determined storage time of 1 microseconds. We can then encode many qubits in short <10 ns temporal modes (time-bin qubits). We show the good coherence of the mapping by simultaneously storing and analyzing multiple time-bin qubits.

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arXiv2010

Efficient optical pumping of Zeeman spin levels in Nd3+:YVO4

We demonstrate that Zeeman ground-state spin levels in Nd3+:YVO4 provides the possibility to create an efficient lambda-system for optical pumping experiments. The branching ratio R in the lambda-system is measured experimentally via absorption spectroscopy and is compared to a theoretical model. We show that R can be tuned by changing the orientation of the magnetic field. These results are applied to optical pumping experiments, where significant improvement is obtained compared to previous experiments in this system. The tunability of the branching ratio in combination with its good coherence properties and the high oscillator strength makes Nd3+:YVO4 an interesting candidate for various quantum information protocols.

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arXiv2010

Demonstration of atomic frequency comb memory for light with spin-wave storage

We present a light-storage experiment in a praseodymium-doped crystal where the light is mapped onto an inhomogeneously broadened optical transition shaped into an atomic frequency comb. After absorption of the light the optical excitation is converted into a spin-wave excitation by a control pulse. A second control pulse reads the memory (on-demand) by reconverting the spin-wave excitation to an optical one, where the comb structure causes a photon-echo type rephasing of the dipole moments and directional retrieval of the light. This combination of photon echo and spin-wave storage allows us to store sub-microsecond (450ns) pulses for up to 20 microseconds. The scheme has a high potential for storing multiple temporal modes in the single photon regime, which is an important resource for future long-distance quantum communication based on quantum repeaters.

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arXiv2009

Electric control of collective atomic coherence in an Erbium doped solid

We demonstrate 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 and the linear Stark effect. The manipulation of atomic coherence is characterized with the collective spontaneous emission (optical free induction decay) 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 free induction decay. Our results show that the use of external electric fields does not introduce any substantial additional decoherence and enables the manipulation of collective atomic coherence with a very high degree of precision on the time scale of tens of ns. This provides an interesting resource for photonic quantum state storage and quantum state manipulation.

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arXiv2009

Multimode quantum memory based on atomic frequency combs

An efficient multi-mode quantum memory is a crucial resource for long-distance quantum communication based on quantum repeaters. We propose a quantum memory based on spectral shaping of an inhomogeneously broadened optical transition into an atomic frequency comb (AFC). The spectral width of the AFC allows efficient storage of multiple temporal modes, without the need to increase the absorption depth of the storage material, in contrast to previously known quantum memories. Efficient readout is possible thanks to rephasing of the atomic dipoles due to the AFC structure. Long-time storage and on-demand readout is achieved by use of spin-states in a lambda-type configuration. We show that an AFC quantum memory realized in solids doped with rare-earth-metal ions could store hundreds of modes or more with close to unit efficiency, for material parameters achievable today.

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arXiv2009

Creating Single Collective Atomic Excitations via Spontaneous Raman Emission in Inhomogeneously Broadened Systems : Beyond the Adiabatic Approximation

The creation of single collective excitations in atomic ensembles via spontaneous Raman emission plays a key role in several quantum communication protocols, starting with the seminal DLCZ protocol [L.-M.Duan, M.D. Lukin, J.I. Cirac, and P. Zoller, Nature {\bf 414}, 413 (2001).] This process is usually analyzed theoretically under the assumptions that the write laser pulse inducing the Raman transition is far off-resonance, and that the atomic ensemble is only homogeneously broadened. Here we study the impact of near-resonance excitation for inhomogeneously broadened ensembles on the collective character of the created atomic excitation. Our results are particularly relevant for experiments with hot atomic gases and for potential future solid-state implementations.

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arXiv2008

A solid state light-matter interface at the single photon level

Coherent and reversible mapping of quantum information between light and matter is an important experimental challenge in quantum information science. In particular, it is a decisive milestone for the implementation of quantum networks and quantum repeaters. So far, quantum interfaces between light and atoms have been demonstrated with atomic gases, and with single trapped atoms in cavities. Here we demonstrate the coherent and reversible mapping of a light field with less than one photon per pulse onto an ensemble of 10 millions atoms naturally trapped in a solid. This is achieved by coherently absorbing the light field in a suitably prepared solid state atomic medium. The state of the light is mapped onto collective atomic excitations on an optical transition and stored for a pre-programmed time up of to 1 mu s before being released in a well defined spatio-temporal mode as a result of a collective interference. The coherence of the process is verified by performing an interference experiment with two stored weak pulses with a variable phase relation. Visibilities of more than 95% are obtained, which demonstrates the high coherence of the mapping process at the single photon level. In addition, we show experimentally that our interface allows one to store and retrieve light fields in multiple temporal modes. Our results represent the first observation of collective enhancement at the single photon level in a solid and open the way to multimode solid state quantum memories as a promising alternative to atomic gases.

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arXiv2007

Quantum Repeaters with Photon Pair Sources and Multi-Mode Memories

We propose a quantum repeater protocol which builds on the well-known DLCZ protocol [L.M. Duan, M.D. Lukin, J.I. Cirac, and P. Zoller, Nature 414, 413 (2001)], but which uses photon pair sources in combination with memories that allow to store a large number of temporal modes. We suggest to realize such multi-mode memories based on the principle of photon echo, using solids doped with rare-earth ions. The use of multi-mode memories promises a speedup in entanglement generation by several orders of magnitude and a significant reduction in stability requirements compared to the DLCZ protocol.

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arXiv2007

Analysis of a quantum memory for photons based on controlled reversible inhomogeneous broadening

We present a detailed analysis of a quantum memory for photons based on controlled and reversible inhomogeneous broadening (CRIB). The explicit solution of the equations of motion is obtained in the weak excitation regime, making it possible to gain insight into the dependence of the memory efficiency on the optical depth, and on the width and shape of the atomic spectral distributions. We also study a simplified memory protocol which does not require any optical control fields.

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arXiv2006

Controlled Stark shifts in Er$^{3+}$-doped crystalline and amorphous waveguides for quantum state storage

We present measurements of the linear Stark effect on the $^{4}$I$_{15/2} \to$ $^{4}$I$_{13/2}$ transition in an Er$^{3+}$-doped proton-exchanged LiNbO$_{3}$ crystalline waveguide and an Er$^{3+}$-doped silicate fiber. The measurements were made using spectral hole burning techniques at temperatures below 4 K. We measured an effective Stark coefficient $(Δμ_{e}χ)/(h)=25\pm1$kHz/Vcm$^{-1}$ in the crystalline waveguide and $(\bar{Δμ_{e}}χ)/(h)=15\pm1$kHz/Vcm$^{-1}$ in the silicate fiber. These results confirm the potential of Erbium doped waveguides for quantum state storage based on controlled reversible inhomogeneous broadening.

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arXiv2006

Investigations of Optical Coherence Properties in an Erbium-doped Silicate Fiber for Quantum State Storage

We studied optical coherence properties of the 1.53 $μ$m telecommunication transition in an Er$^{3+}$-doped silicate optical fiber through spectral holeburning and photon echoes. We find decoherence times of up to 3.8 $μ$s at a magnetic field of 2.2 Tesla and a temperature of 150 mK. A strong magnetic-field dependent optical dephasing was observed and is believed to arise from an interaction between the electronic Er$^{3+}$ spin and the magnetic moment of tunneling modes in the glass. Furthermore, we observed fine-structure in the Erbium holeburning spectrum originating from superhyperfine interaction with $^{27}$Al host nuclei. Our results show that Er$^{3+}$-doped silicate fibers are promising material candidates for quantum state storage.

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