Coherently driving a single quantum two-level system with dichromatic laser pulses


The excitation of individual two-level quantum systems using an electromagnetic field is an elementary tool of quantum optics, with widespread applications across quantum technologies. The efficient excitation of a single two-level system usually requires the driving field to be at the same frequency as the transition between the two quantum levels. However, in solid-state implementations, the scattered laser light can dominate over the single photons emitted by the two-level system, imposing a challenge for single-photon sources. Here, we propose a background-free method for the coherent excitation and control of a two-level quantum system using a phase-locked dichromatic electromagnetic field with no spectral overlap with the optical transition. We demonstrate this method experimentally by stimulating single-photon emission from a single quantum dot embedded in a micropillar, reaching single-photon purity of 0.988(1) and indistinguishability of 0.962(6). The phase-coherent nature of our two-colour excitation scheme is demonstrated by the dependence of the resonance fluorescence intensity on the relative phase between the two pulses. Our two-colour excitation method represents an additional and useful tool for the study of atom–photon interaction, and the generation of spectrally isolated indistinguishable single photons.

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Fig. 1: Coherent driving of a single two-level system with dichromatic pulses.
Fig. 2: Generation of dichromatic pulses using a 4f optical system.
Fig. 3: Single-photon intensity as a function of the driving strength.
Fig. 4: Phase-dependent resonance fluorescence under dichromatic driving.
Fig. 5: Characterization of the single-photon source under two-colour excitation.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.


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The National Natural Science Foundation of China, the Chinese Academy of Science, Anhui Initiative in Quantum Information Technologies, the Science and Technology Commission of Shanghai Municipality, the National Fundamental Research Program and the State of Bavaria supported this work. M.A. is supported by an ERC Consolidator Grant PHOENICS (no. 617985), and the EPSRC Quantum Technology Hub NQIT (EP/M013243/1). C.S. acknowledges support by the DFG within the project SCHN1376 5-1.

Author information

C.-Y.L. and J.-W.P. conceived the idea and designed the experiment. C.S. and S.H. grew the quantum dot samples. Y.-M.H., H.W., C.W., X.D., J.Q., Z.-C.D., S.C., J.-P.L., R.-Z.L. and C.-Y.L. performed the experiment. C.W., M.-C.C., M.A. and C.-Y.L. performed theoretical modelling and analysed the experimental data. C.-Y.L. wrote the paper with input from all authors. C.-Y.L. and J.-W.P. supervised the whole project.

Correspondence to Chao-Yang Lu or Jian-Wei Pan.

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