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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

Incoherent photon contribution.The probability to read out incoherent photons (p1) normalized by the fraction of atoms () that have been incoherently transferred to the readout state (/1〉) as a function of the linewidth, κ2 of the filter cavity.  essentially only depends on  and κ2 for the parameters that we are considering, which are , an optical depth of 168 and a finesse of the cell cavity in the range 20–100. Furthermore, we have assumed that , which ensures a temporal filtering of the incoherent photons while keeping a high readout efficiency of the coherent photons. The plot was obtained by numerically simulating the Cs-cells used in the proof-of-principle experiment including the full-level structure of the Cs-atoms.
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f5: Incoherent photon contribution.The probability to read out incoherent photons (p1) normalized by the fraction of atoms () that have been incoherently transferred to the readout state (/1〉) as a function of the linewidth, κ2 of the filter cavity. essentially only depends on and κ2 for the parameters that we are considering, which are , an optical depth of 168 and a finesse of the cell cavity in the range 20–100. Furthermore, we have assumed that , which ensures a temporal filtering of the incoherent photons while keeping a high readout efficiency of the coherent photons. The plot was obtained by numerically simulating the Cs-cells used in the proof-of-principle experiment including the full-level structure of the Cs-atoms.

Mentions: Atoms can also be in the readout state /1〉 either by inefficient optical pumping or by wall collisions. These atoms will mainly produce ‘incoherent' photons. The incoherent photons will have a much broader temporal and frequency profile than the ‘coherent' photons originating from the symmetric excitation. We can thus to some extent filter them from the coherent photons by sending the light through a filter cavity, which makes a spectral filtering, as well as having a not too long readout time τread, which makes a temporal filter. In addition to the incoherent photons, atoms incoherently prepared in the wrong state can also produce coherent photons because the incoherent atoms have an overlap with the symmetric mode. If a fraction of the atoms are transferred to the state /1〉, the probability to read out a coherent single photon from these atoms is . The probability p1 to read out an incoherent photon can be found to lowest order by assuming that an excitation is stored in any asymmetric mode instead of the symmetric Dicke mode in the perturbative expansion of described above. Doing the perturbative expansion, we then get a contribution to acell from these incoherent excitations to the first-order term a1. From this, we can find the number of incoherent photons in the retrieval. We have evaluated p1 by numerical simulating the Cs-cells as for the readout (see Supplementary Methods). Figure 5 shows as a function of the linewidth (κ2) of the filter cavity. We have assumed that as in Fig. 3b. Note that this choice of readout time ensures a high readout efficiency while still making a temporal filtering of the incoherent photons since these have a smaller readout rate and hence predominantly arrive later. It is seen that for κ2≈2π·80 kHz. With a linewidth of the filter cavity more narrow than this, the error will thus be dominated by the coherent photons which are emitted with a probability . Imposing this linewidth of the filter cavity for the numerical example for the readout efficiency given above for a readout time of t=200 μs, would make it drop from ≈90% to ≈86%. Hence, we lose only a little on the readout efficiency by filtering out the incoherent photons. Experimentally, it will be simpler to use the same filter cavity for the retrieval as for the write process, and hence it may be desirable to use a more narrow filter cavity to have an efficient write process (see Fig. 3b). In this case one can use a longer read out time to suppress loss from the filter cavity. After filtering out the incoherent photons, the remaining error is caused by coherent photons from atoms being incoherently prepared in the wrong state. This error is equal to the probability that an atom is in the wrong state.


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)

Incoherent photon contribution.The probability to read out incoherent photons (p1) normalized by the fraction of atoms () that have been incoherently transferred to the readout state (/1〉) as a function of the linewidth, κ2 of the filter cavity.  essentially only depends on  and κ2 for the parameters that we are considering, which are , an optical depth of 168 and a finesse of the cell cavity in the range 20–100. Furthermore, we have assumed that , which ensures a temporal filtering of the incoherent photons while keeping a high readout efficiency of the coherent photons. The plot was obtained by numerically simulating the Cs-cells used in the proof-of-principle experiment including the full-level structure of the Cs-atoms.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: Incoherent photon contribution.The probability to read out incoherent photons (p1) normalized by the fraction of atoms () that have been incoherently transferred to the readout state (/1〉) as a function of the linewidth, κ2 of the filter cavity. essentially only depends on and κ2 for the parameters that we are considering, which are , an optical depth of 168 and a finesse of the cell cavity in the range 20–100. Furthermore, we have assumed that , which ensures a temporal filtering of the incoherent photons while keeping a high readout efficiency of the coherent photons. The plot was obtained by numerically simulating the Cs-cells used in the proof-of-principle experiment including the full-level structure of the Cs-atoms.
Mentions: Atoms can also be in the readout state /1〉 either by inefficient optical pumping or by wall collisions. These atoms will mainly produce ‘incoherent' photons. The incoherent photons will have a much broader temporal and frequency profile than the ‘coherent' photons originating from the symmetric excitation. We can thus to some extent filter them from the coherent photons by sending the light through a filter cavity, which makes a spectral filtering, as well as having a not too long readout time τread, which makes a temporal filter. In addition to the incoherent photons, atoms incoherently prepared in the wrong state can also produce coherent photons because the incoherent atoms have an overlap with the symmetric mode. If a fraction of the atoms are transferred to the state /1〉, the probability to read out a coherent single photon from these atoms is . The probability p1 to read out an incoherent photon can be found to lowest order by assuming that an excitation is stored in any asymmetric mode instead of the symmetric Dicke mode in the perturbative expansion of described above. Doing the perturbative expansion, we then get a contribution to acell from these incoherent excitations to the first-order term a1. From this, we can find the number of incoherent photons in the retrieval. We have evaluated p1 by numerical simulating the Cs-cells as for the readout (see Supplementary Methods). Figure 5 shows as a function of the linewidth (κ2) of the filter cavity. We have assumed that as in Fig. 3b. Note that this choice of readout time ensures a high readout efficiency while still making a temporal filtering of the incoherent photons since these have a smaller readout rate and hence predominantly arrive later. It is seen that for κ2≈2π·80 kHz. With a linewidth of the filter cavity more narrow than this, the error will thus be dominated by the coherent photons which are emitted with a probability . Imposing this linewidth of the filter cavity for the numerical example for the readout efficiency given above for a readout time of t=200 μs, would make it drop from ≈90% to ≈86%. Hence, we lose only a little on the readout efficiency by filtering out the incoherent photons. Experimentally, it will be simpler to use the same filter cavity for the retrieval as for the write process, and hence it may be desirable to use a more narrow filter cavity to have an efficient write process (see Fig. 3b). In this case one can use a longer read out time to suppress loss from the filter cavity. After filtering out the incoherent photons, the remaining error is caused by coherent photons from atoms being incoherently prepared in the wrong state. This error is equal to the probability that an atom is in the wrong state.

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