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Register a new userEntangled Photons Enabled Time- and Frequency-Resolved Coherent Raman Spectroscopy in Condensed Phase Molecules
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We develop an ultrafast frequency-resolved Raman spectroscopy with entangled photons for polyatomic molecules in condensed phases, to probe the electronic and vibrational coherences. Using quantum correlation between the photons, the signal shows the capability of both temporal and spectral resolutions that are not accessible by either classical pulses or the fields without entanglement. We develop a microscopic theory for this Raman spectroscopy, revealing the electronic coherence dynamics which often shows a rapid decay within $sim$50fs. The heterodyne-detected Raman signal is further developed to capture the phases of electronic coherence and emission in real-time domain.
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Pairs of photons entangled in their time-frequency degree of freedom are of great interest in quantum optics research and applications, due to their relative ease of generation and their high capacity for encoding information. Here we analyze, both theoretically and experimentally, the behavior of phase-insensitive spectrally-resolved interferences arising from two pairs of time-frequency entangled photons. At its core, this is a multimode entanglement swapping experiment, whereby a spectrally resolved joint measurement on the idler photons from both pairs results in projecting the signal photons onto a Bell state whose form depends on the measurement outcome. Our analysis is a thorough exploration of what can be achieved using time-frequency entanglement and spectrally-resolved Bell-state measurements.
Time-bin entangled photons are ideal for long-distance quantum communication via optical fibers. Here we present a source where, even at high creation rates, each excitation pulse generates at most one time-bin entangled pair. This is important for the accuracy and security of quantum communication. Our site-controlled quantum dot generates single polarization-entangled photon pairs, which are then converted, without loss of entanglement strength, into single time-bin entangled photon pairs.
Long distance quantum communication is one of the prime goals in the field of quantum information science. With information encoded in the quantum state of photons, existing telecommunication fiber networks can be effectively used as a transport medium. To achieve this goal, a source of robust entangled single photon pairs is required. While time-bin entanglement offers the required robustness, currently used parametric down-conversion sources have limited performance due to multi-pair contributions. We report the realization of a source of single time-bin entangled photon pairs utilizing the biexciton-exciton cascade in a III/V self-assembled quantum dot. We analyzed the generated photon pairs by an inherently phase-stable interferometry technique, facilitating uninterrupted long integration times. We confirmed the entanglement by performing a quantum state tomography of the emitted photons, which yielded a fidelity of 0.69(3) and a concurrence of 0.41(6).
A theory of correlations between N photons of given frequencies and detected at given time delays is presented. These correlation functions are usually too cumbersome to be computed explicitly. We show that they are obtained exactly through intensity correlations between two-level sensors in the limit of their vanishing coupling to the system. This allows the computation of correlation functions hitherto unreachable. The uncertainties in time and frequency of the detection, which are necessary variables to describe the system, are intrinsic to the theory. We illustrate the formalism with the Jaynes--Cummings model, showing how correlations of various peaks at zero or finite time delays bring new insights into the dynamics of open quantum systems.
Time-resolved Raman spectroscopy has been applied to probe the anharmonic coupling and electron-phonon interaction of optical phonons in graphite. From the decay of the transient anti-Stokes scattering of the G-mode following ultrafast excitation, we measured a lifetime of 2.2+/-0.1ps for zone-center optical phonons. We also observed a transient stiffening of G-mode phonons, an effect attributed to the reduction of the electron-phonon coupling for high electronic temperatures.
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