Photon indistinguishability measurements under pulsed and continuous excitation

The indistinguishability of successively generated photons from a single quantum emitter is most commonly measured using two-photon interference at a beam splitter. Whilst for sources excited in the pulsed regime the measured bunching of photons reflects the full wavepacket indistinguishability of the emitted photons, for continuous wave (cw) excitation the inevitable dependence on detector timing resolution and driving strength obscures the underlying photon interference process. Here we derive a method to extract the photon indistinguishability from cw measurements by considering the relevant correlation functions. The equivalence of both methods is experimentally verified through comparison of cw and pulsed excitation of an archetypal source of photons, a single molecule

Entangled-State Cycles of Atomic Collective-Spin States

We study quantum trajectories of collective atomic spin states of $N$ effective two-level atoms driven with laser and cavity fields. We show that interesting ``entangled-state cycles'' arise probabilistically when the (Raman) transition rates between the two atomic levels are set equal. For odd (even) $N$, there are $(N+1)/2$ ($N/2$) possible cycles. During each cycle the $N$-qubit state switches, with each cavity photon emission, between the states $(|N/2,m>\pm |N/2,-m>)/\sqrt{2}$, where $|N/2,m>$ is a Dicke state in a rotated collective basis. The quantum number $m$ ($>0$), which distinguishes the particular cycle, is determined by the photon counting record and varies randomly from one trajectory to the next. For even $N$ it is also possible, under the same conditions, to prepare probabilistically (but in steady state) the Dicke state $|N/2,0>$, i.e., an $N$-qubit state with $N/2$ excitations, which is of particular interest in the context of multipartite entanglement.Comment: 10 pages, 9 figure

Data to accompany C. Clear et al., "Phonon-induced optical dephasing in single organic molecules," Phys. Rev. Lett. (2020)

Data to accompany C. Clear, R. C. Schofield, K. D. Major, J. Iles-Smith, A. S. Clark, and D. P. S. McCutcheon "Phonon-induced optical dephasing in single organic molecules," Phys. Rev. Lett. 124, 153602 (2020). The raw data for single molecule spectra, second-order correlation functions, fluorescence excitation spectra, and time-correlated single photon counting, can be imported using the included Mathematica notebook which also contains instructions.Data to accompany C. Clear, R. C. Schofield, K. D. Major, J. Iles-Smith, A. S. Clark, and D. P. S. McCutcheon "Phonon-induced optical dephasing in single organic molecules," Phys. Rev. Lett. 124, 153602 (2020). The raw data for single molecule spectra, second-order correlation functions, fluorescence excitation spectra, and time-correlated single photon counting, can be imported using the included Mathematica notebook which also contains instructions.