Multimode quantum memory based on atomic frequency combs

Question

1. What are the contributions mentioned in the paper "Multimode quantum memory based on atomic frequency combs" ?

2. What can be done to create more complicated structures in frequency space?

3. What is the effect of the interference effect on the output amplitude?

4. What is the spectral distribution of the AFC?

Accepted Answer

The authors propose a quantum memory based on spectral shaping of an inhomogeneously broadened optical transition into an atomic frequency comb ( AFC ).. The authors 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.

Accepted Answer

Moreover a time-domain approach can be used for creating more complicated structures in frequency space, for instance multiple AFCs having different periodicity.

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Even though there is absorption along the path, there is a constructive interference effect which leads to the output amplitude potentially being arbitrarily close in magnitude to the input amplitude for large enough ̃L .

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If the atomic density integrated over the photon bandwidth is high enough, the photon can be totally absorbed by the AFC although the spectral density of atoms is concentrated to narrow peaks.

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The g - e transition is spectrally shaped such that the atomic density function consists of a series of narrow peaks spanning a large frequency range, which the authors call an atomic frequency comb AFC .

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one could then store 100 temporal modes in one single QM with an efficiency of 90%, which the authors verified by numerically simulating storage of 100 modes using the parameters above.

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But if the peak absorption depth d of the comb is high enough, the total density of atoms in the comb can still be sufficiently high to absorb the input mode with close to 100% probability.

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By applying the two counterpropagating control fields, the spatial phase pattern of the atomic polarization changes such that it couples with the backward propagating field mode 15,16,29 .

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A complete storage experiment including transfer to the spin state will be affected by the limitation in spin coherence time, for Eu3+ :Y2SiO5 T2spin=36 ms 41 has been observed so far, and by the transfer efficiency of the control fields cf. discussion above .

Accepted Answer

4The comb absorption is thus reduced by a factor of 1 /F, which is to be expected since the total density of atoms in the comb integrated over the frequency bandwidth of the photon is reduced by a factor of 1 /F in the preparation step.

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The matter part was assumed to be an ensemble of twolevel atoms, including levels g and e in Fig. 1, and the light field was treated as a one-dimensional spatial mode.

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This causes a spectral averaging of the sharp AFC structure into a smooth distribution, allowing for uniform absorption over the photons bandwidth see also Sec. III .

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It follows that the collective state is re-established after a time 2 / , which leads to a coherent photon-echo 25–27 type re-emission in the forward direction.

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The decay of the re-emitted field amplitude is given by the Fourier transform of a peak in the comb see Eq. A6 and discussion preceding Eq. A16 , in analogy with the role of the initial peak shape in the CRIB quantum memory protocol 29,30 .

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If the authors assume that the spin transition is completely homogeneous, the storage time is only limited by the coherence lifetime of the spin wave.

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As the authors will show below, the efficiency of the storage for backward retrieval can theoretically approach unity for high optical depths.

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The two counterpropagating control fields were modeled by transferring the forward atomic mode, associated with the forward propagating optical mode, to a backward atomic mode 29 .

Accepted Answer

In the case of EIT even larger d would be necessary due to worse scaling as mentioned in Sec. I. The AFC only requires d =40 to reach the same efficiency, independently of N.

Multimode quantum memory based on atomic frequency combs

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Most frequently asked questions

1. What are the contributions mentioned in the paper "Multimode quantum memory based on atomic frequency combs" ?

2. What can be done to create more complicated structures in frequency space?

3. What is the effect of the interference effect on the output amplitude?

4. What is the spectral distribution of the AFC?

5. What is the atomic density function of a comb?

6. How many modes could be stored in one single QM?

7. How many atoms can absorb the input mode?

8. What is the effect of the two counterpropagating control fields?

9. What is the effect of the limitation in spin coherence time?

10. How much is the absorption of the comb reduced?

11. What is the atomic evolution of the matter part?

12. What is the spectral distribution of the sharp AFC structure?

13. What is the re-emission of the collective state?

14. What is the role of the initial peak shape in the CRIB protocol?

15. How long is the storage time for the collective state?

16. What is the efficiency of the storage for backward retrieval?

17. How did the two counterpropagating control fields be modeled?

18. How much d is required to reach the same efficiency?

Figures

Citations

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References

Initial Experiments Concerning Quantum Information Processing in Rare-Earth-Ion Doped Crystals

Spectrally programmed stimulated photon echo.

Temporally programmed free-induction decay

Chirped pulse generation of a narrow absorption line in a Tm3+:YAG crystal

Mapping broadband single-photon wave packets into an atomic memory

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