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Scalable photonic network architecture based on motional averaging in room temperature gas.

Borregaard J, Zugenmaier M, Petersen JM, Shen H, Vasilakis G, Jensen K, Polzik ES, Sørensen AS - Nat Commun (2016)

Bottom Line: Thermal atomic vapours, which present a simple and scalable resource, have only been used for continuous variable processing or for discrete variable processing on short timescales where atomic motion is negligible.Here we develop a theory based on motional averaging to enable room temperature discrete variable quantum memories and coherent single-photon sources.We demonstrate the feasibility of this approach to scalable quantum memories with a proof-of-principle experiment with room temperature atoms contained in microcells with spin-protecting coating, placed inside an optical cavity.

View Article: PubMed Central - PubMed

Affiliation: The Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen Ø DK-2100, Denmark.

ABSTRACT
Quantum interfaces between photons and atomic ensembles have emerged as powerful tools for quantum technologies. Efficient storage and retrieval of single photons requires long-lived collective atomic states, which is typically achieved with immobilized atoms. Thermal atomic vapours, which present a simple and scalable resource, have only been used for continuous variable processing or for discrete variable processing on short timescales where atomic motion is negligible. Here we develop a theory based on motional averaging to enable room temperature discrete variable quantum memories and coherent single-photon sources. We demonstrate the feasibility of this approach to scalable quantum memories with a proof-of-principle experiment with room temperature atoms contained in microcells with spin-protecting coating, placed inside an optical cavity. The experimental conditions correspond to a few photons per pulse and a long coherence time of the forward scattered photons is demonstrated, which is the essential feature of the motional averaging.

No MeSH data available.


Related in: MedlinePlus

PSD of the emitted light.The figure shows both the experimental data and the simulation of the PSD. The broad feature originates from short-time, incoherent light–atom interaction, while the sharp peak is from the long-time, coherent light–atom interaction. The optical scattering was obtained through the Faraday effect and is centred around the Larmor frequency at 823.8 kHz (the single high point in the figure). The simulations have been rescaled to coincide with the data at this point. In the simulations, we include the possibility of atoms being trapped in the coating of the cell walls. From the figure, we estimate that such trapping time is below 0.1 μs and can thus be ignored. The cell used in the experiment had dimensions 2L × 2L × 2Lz with L=150 μm and Lz=0.5 cm and the light beam had a Gaussian profile with a waist of 55 μm. The statistical uncertainty of each experimental point is very small and is therefore not shown.
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f2: PSD of the emitted light.The figure shows both the experimental data and the simulation of the PSD. The broad feature originates from short-time, incoherent light–atom interaction, while the sharp peak is from the long-time, coherent light–atom interaction. The optical scattering was obtained through the Faraday effect and is centred around the Larmor frequency at 823.8 kHz (the single high point in the figure). The simulations have been rescaled to coincide with the data at this point. In the simulations, we include the possibility of atoms being trapped in the coating of the cell walls. From the figure, we estimate that such trapping time is below 0.1 μs and can thus be ignored. The cell used in the experiment had dimensions 2L × 2L × 2Lz with L=150 μm and Lz=0.5 cm and the light beam had a Gaussian profile with a waist of 55 μm. The statistical uncertainty of each experimental point is very small and is therefore not shown.

Mentions: Initially, all atoms are pumped to a stable ground state /0〉 (see Fig. 1). In the ‘write' process, the objective is to create a single, collective excitation in the ensemble, thereby creating the symmetric Dicke state , with where j is the atom number, N is the total number of atoms and /1〉 is another stable ground state in the atoms. The /0〉→/e〉 transition is driven with a laser pulse, which is far-detuned from the atomic transition to suppress the effect of the Doppler broadening of the atomic levels and absorption. In addition, the pulse should be sufficiently weak such that multiple excitations in the ensemble can be neglected. The write process is conditioned on detecting a single photon (quantum photon) emitted in a Raman transition /0〉→/e〉→/1〉. Upon detection, the atomic state is projected into the symmetric Dicke state if the light experienced a homogeneous interaction with all atoms, that is, if the probability for different atoms to have emitted the photon is equal. In a realistic setup, the laser beam does not fill the entire cell and only atoms that are in the beam contribute to the cavity field, resulting in an asymmetric spin wave being created. Atoms leaving the beam will, however, return to the beam due to the frequent collisions with the cell walls. During the collisions, the atomic state is preserved because of the alkene coating of the cells and we exploit this to make a motional averaging of the light–atom interaction. If the interaction time is long enough to allow the atoms to move in and out of the beam several times, they will on average have experienced the same interaction with the light. Consequently, the detection of a cavity photon will, to a good approximation, project the atomic state to a Dicke state. Since the cell cavity has a limited finesse, it may, in practice, not have a sufficiently narrow linewidth to allow this averaging. We therefore introduce an external filter cavity. As we show below, the output from the cell cavity consists of a spectrally narrow coherent component and a broad incoherent component (see Fig. 2). By selecting out the coherent part, the filter cavity effectively increases the interaction time and allows for motional averaging. At the same time, the filter cavity can also separate the quantum photon from the classical drive if there is a small frequency difference between the two, such that only one frequency is resonant in the filter cavity while both are sustained in the cell cavity. Furthermore, choosing the frequency difference to be an even number of free spectral ranges of the cell cavity ensures an overlap of the field modes at the centre of the cavity, such that atoms can interact simultaneously with both modes if the length of the microcell is small compared with the wavelength corresponding to the frequency difference (see Supplementary Methods and Supplementary Fig. 1).


Scalable photonic network architecture based on motional averaging in room temperature gas.

Borregaard J, Zugenmaier M, Petersen JM, Shen H, Vasilakis G, Jensen K, Polzik ES, Sørensen AS - Nat Commun (2016)

PSD of the emitted light.The figure shows both the experimental data and the simulation of the PSD. The broad feature originates from short-time, incoherent light–atom interaction, while the sharp peak is from the long-time, coherent light–atom interaction. The optical scattering was obtained through the Faraday effect and is centred around the Larmor frequency at 823.8 kHz (the single high point in the figure). The simulations have been rescaled to coincide with the data at this point. In the simulations, we include the possibility of atoms being trapped in the coating of the cell walls. From the figure, we estimate that such trapping time is below 0.1 μs and can thus be ignored. The cell used in the experiment had dimensions 2L × 2L × 2Lz with L=150 μm and Lz=0.5 cm and the light beam had a Gaussian profile with a waist of 55 μm. The statistical uncertainty of each experimental point is very small and is therefore not shown.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4834638&req=5

f2: PSD of the emitted light.The figure shows both the experimental data and the simulation of the PSD. The broad feature originates from short-time, incoherent light–atom interaction, while the sharp peak is from the long-time, coherent light–atom interaction. The optical scattering was obtained through the Faraday effect and is centred around the Larmor frequency at 823.8 kHz (the single high point in the figure). The simulations have been rescaled to coincide with the data at this point. In the simulations, we include the possibility of atoms being trapped in the coating of the cell walls. From the figure, we estimate that such trapping time is below 0.1 μs and can thus be ignored. The cell used in the experiment had dimensions 2L × 2L × 2Lz with L=150 μm and Lz=0.5 cm and the light beam had a Gaussian profile with a waist of 55 μm. The statistical uncertainty of each experimental point is very small and is therefore not shown.
Mentions: Initially, all atoms are pumped to a stable ground state /0〉 (see Fig. 1). In the ‘write' process, the objective is to create a single, collective excitation in the ensemble, thereby creating the symmetric Dicke state , with where j is the atom number, N is the total number of atoms and /1〉 is another stable ground state in the atoms. The /0〉→/e〉 transition is driven with a laser pulse, which is far-detuned from the atomic transition to suppress the effect of the Doppler broadening of the atomic levels and absorption. In addition, the pulse should be sufficiently weak such that multiple excitations in the ensemble can be neglected. The write process is conditioned on detecting a single photon (quantum photon) emitted in a Raman transition /0〉→/e〉→/1〉. Upon detection, the atomic state is projected into the symmetric Dicke state if the light experienced a homogeneous interaction with all atoms, that is, if the probability for different atoms to have emitted the photon is equal. In a realistic setup, the laser beam does not fill the entire cell and only atoms that are in the beam contribute to the cavity field, resulting in an asymmetric spin wave being created. Atoms leaving the beam will, however, return to the beam due to the frequent collisions with the cell walls. During the collisions, the atomic state is preserved because of the alkene coating of the cells and we exploit this to make a motional averaging of the light–atom interaction. If the interaction time is long enough to allow the atoms to move in and out of the beam several times, they will on average have experienced the same interaction with the light. Consequently, the detection of a cavity photon will, to a good approximation, project the atomic state to a Dicke state. Since the cell cavity has a limited finesse, it may, in practice, not have a sufficiently narrow linewidth to allow this averaging. We therefore introduce an external filter cavity. As we show below, the output from the cell cavity consists of a spectrally narrow coherent component and a broad incoherent component (see Fig. 2). By selecting out the coherent part, the filter cavity effectively increases the interaction time and allows for motional averaging. At the same time, the filter cavity can also separate the quantum photon from the classical drive if there is a small frequency difference between the two, such that only one frequency is resonant in the filter cavity while both are sustained in the cell cavity. Furthermore, choosing the frequency difference to be an even number of free spectral ranges of the cell cavity ensures an overlap of the field modes at the centre of the cavity, such that atoms can interact simultaneously with both modes if the length of the microcell is small compared with the wavelength corresponding to the frequency difference (see Supplementary Methods and Supplementary Fig. 1).

Bottom Line: Thermal atomic vapours, which present a simple and scalable resource, have only been used for continuous variable processing or for discrete variable processing on short timescales where atomic motion is negligible.Here we develop a theory based on motional averaging to enable room temperature discrete variable quantum memories and coherent single-photon sources.We demonstrate the feasibility of this approach to scalable quantum memories with a proof-of-principle experiment with room temperature atoms contained in microcells with spin-protecting coating, placed inside an optical cavity.

View Article: PubMed Central - PubMed

Affiliation: The Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen Ø DK-2100, Denmark.

ABSTRACT
Quantum interfaces between photons and atomic ensembles have emerged as powerful tools for quantum technologies. Efficient storage and retrieval of single photons requires long-lived collective atomic states, which is typically achieved with immobilized atoms. Thermal atomic vapours, which present a simple and scalable resource, have only been used for continuous variable processing or for discrete variable processing on short timescales where atomic motion is negligible. Here we develop a theory based on motional averaging to enable room temperature discrete variable quantum memories and coherent single-photon sources. We demonstrate the feasibility of this approach to scalable quantum memories with a proof-of-principle experiment with room temperature atoms contained in microcells with spin-protecting coating, placed inside an optical cavity. The experimental conditions correspond to a few photons per pulse and a long coherence time of the forward scattered photons is demonstrated, which is the essential feature of the motional averaging.

No MeSH data available.


Related in: MedlinePlus