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Register a new userIndistinguishability of independent single photons
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The indistinguishability of independent single photons is presented by decomposing the single photon pulse into the mixed state of different transform limited pulses. The entanglement between single photons and outer environment or other photons induces the distribution of the center frequencies of those transform limited pulses and makes photons distinguishable. Only the single photons with the same transform limited form are indistinguishable. In details, the indistinguishability of single photons from the solid-state quantum emitter and spontaneous parametric down conversion is examined with two-photon Hong-Ou-Mandel interferometer. Moreover, experimental methods to enhance the indistinguishability are discussed, where the usage of spectral filter is highlighted.
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Generation and manipulation of the quantum state of a single photon is at the heart of many quantum information protocols. There has been growing interest in using phase modulators as quantum optics devices that preserve coherence. In this Letter, we have used an electro-optic phase modulator to shape the state vector of single photons emitted by a quantum dot to generate new frequency components (modes) and explicitly demonstrate that the phase modulation process agrees with the theoretical prediction at a single photon level. Through two-photon interference measurements we show that for an output consisting of three modes (the original mode and two sidebands), the indistinguishability of the mode engineered photon, measured through the secondorder intensity correlation (g2(0)) is preserved. This work demonstrates a robust means to generate a photonic qubit or more complex state (e.g., a qutrit) for quantum communication applications by encoding information in the sidebands without the loss of coherence.
We create independent, synchronized single-photon sources with built-in quantum memory based on two remote cold atomic ensembles. The synchronized single photons are used to demonstrate efficient generation of entanglement. The resulting entangled photon pairs violate a Bells Inequality by 5 standard deviations. Our synchronized single photons with their long coherence time of 25 ns and the efficient creation of entanglement serve as an ideal building block for scalable linear optical quantum information processing.
In the present work, the effect of resonant pumping schemes in improving the photon coherence is investigated on InAs/InGaAs/GaAs quantum dots emitting in the telecom C-band. The linewidths of transitions of multiple exemplary quantum dots are determined under above-band pumping and resonance fluorescence via Fourier-transform spectroscopy and resonance scans, respectively. The average linewidth is reduced from $9.74,mathrm{GHz}$ in above-band excitation to $3.50,mathrm{GHz}$ in resonance fluorescence underlining its superior coherence properties. Furthermore, the feasibility of coherent state preparation with a fidelity of $49.2,%$ is demonstrated, constituting a step towards on-demand generation of coherent, single C-band photons from quantum dots. Finally, two-photon excitation of the biexciton is investigated as a resonant pumping scheme. A deconvoluted single-photon purity value of $g^{(2)}_{mathrm{HBT}}(0)=0.072pm 0.104$ and a degree of indistinguishability of $V_{mathrm{HOM}}=0.894pm0.109$ are determined for the biexciton transition. This represents an important step towards fulfilling the prerequisites for quantum communication applications like quantum repeater schemes at telecom wavelength.
The distinguishability of quantum states is important in quantum information theory and has been considered by authors. However, there were no general results considering whether a set of indistinguishable states become distinguishable by viewing them in a larger system without employing extra resources. In this paper, we consider this question for LOCC$_{1}$, PPT and SEP distinguishabilities of states. We use mathematical methods to show that if a set of states is indistinguishable in $otimes _{k=1}^{K} C^{d _{k}}$, then it is indistinguishable even being viewed in $otimes _{k=1}^{K} C^{d _{k}+h _{k}}$, where $K, d _{k}geqslant2$, $h _{k}geqslant0$ are integers. This shows that LOCC$_{1}$, PPT and SEP distinguishabilities of states are properties of states themselves and independent of the dimension of quantum system. With these results, we can give the maximal number of states which can be distinguished via LOCC$_{1}$ and construct a LOCC indistinguishable basis of product states in a general system. Note that our results are also suitable for unambiguous discriminations. Also, we give a conjecture for other distinguishabilities and a framework by defining the Local-global indistinguishable property. Instead of considering such problems for special sets or special systems, we consider the problems for general states in general systems, which have not been considered yet, for our knowledge.
Remote spatial indistinguishability of identical subsystems as a direct controllable quantum resource at distant sites has not been yet experimentally proven. We design a setup capable to tune the spatial indistinguishability of two photons by independently adjusting their spatial distribution in two distant regions, which leads to polarization entanglement starting from uncorrelated photons. The amount of entanglement uniquely depends on the degree of remote spatial indistinguishability, quantified by an entropic measure $mathcal{I}$, which enables teleportation with fidelities above the classical threshold. This experiment realizes a basic nonlocal entangling gate by the inherent nature of identical quantum subsystems.
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