Direct Generation of Tailored Pulse-Mode Entanglement

Abstract

Photonic quantum technology increasingly uses frequency encoding to enable higher quantum information density and noise resilience. Pulsed time-frequency modes (TFM) represent a unique class of spectrally encoded quantum states of light that enable a complete framework for quantum information processing. Here, we demonstrate a technique for direct generation of entangled TFMencoded states in single-pass, tailored downconversion processes. We achieve unprecedented quality in state generation-high rates, heralding efficiency and state fidelity-as characterised via highly resolved time-of-flight fibre spectroscopy and two-photon interference. We employ this technique in a four-photon entanglement swapping scheme as a primitive for TFM-encoded quantum protocols.Generating entanglement in intrinsically highdimensional degrees of freedom of light, such as transverse and longitudinal spatial modes [1,2], or time and frequency, constitutes a powerful resource for photonic quantum technologies-photons that carry more information enable more efficient protocols [3,4]. Time-frequency encoding is intrinsically suitable for waveguide integration and fibre transmission [5,6], making it a promising choice for practical, high-dimensional quantum applications.Quantum information can be encoded either in discrete temporal or spectral modes (namely time-and frequency-bin encoding [6-9]) or in the spectral envelope of the singlephoton wavepackets-time-frequency mode (TFM) encoding [5,10]. TFM-encoded states arise naturally in parametric downconversion (PDC) sources, as TFMs are eigenstates of the PDC process and they span an infinite-dimensional Hilbert space. Conveniently, TFMs possess highly desirable properties: being centred around a target wavelength makes them compatible with fibre networks, they are robust against noise [11] and chromatic dispersion [12], their pulsed nature enables synchronisation and therefore multi-photon protocols and they offer intrinsically high dimensionality [10]. Manipulation and detection of TFMs is enabled by the quantum-pulse toolbox, where sum-and difference-frequency generation are used for reshaping and projecting the quantum states [5,10]. However, generating entangled TFMs in a controlled way can be very challenging [13][14][15][16][17], limiting their usefulness in realistic scenarios. Here, we overcome this problem exploiting domain-engineered nonlinear crystals [18,19] for generating TFM entanglement from standard ultrafast laser pulses in a single-pass PDC experiment. We experimentally validate this technique by benchmarking a maximally antisymmetric state at telecom wavelength † These two authors contributed equally.with near unity fidelity, and implement a four-photon entanglement swapping scheme. Our work complements the pulse-gate toolbox [5,10] for TFM quantum information processing, and establishes a standard for the generation of TFM quantum states of light while paving the way for more complex frequency encoding.In a PDC process, a pump photon probabilistically downconverts into t...

Anyonic two-photon statistics with a semiconductor chip

“…This is a key asset of our approach compared to alternative recently reported schemes based e.g. on nonlinear domain engineering [36,37], that produce high-quality but non-reconfigurable frequencyentangled quantum states, or spectral shaping of the pump spot [38][39][40], which is reconfigurable but cannot modify the wavefunction symmetry and exchange statistics of the photon pairs. Also, in contrast to quantum walks of correlated photons [17][18][19] where the exchange statistics is studied through the spatial correlations at zero delay, here the temporal dependence of two-photon interference, with its peculiar point-symmetry typical of anyons, is revealed (Fig.…”

Spectrally resolved four-photon interference of time-frequency-entangled photons

“…To verify that the heralded state |Ψ jk is indeed entangled, beyond classical correlation, two-photon interference is used in a manner analogous to Refs. [14,15].…”

Measuring higher-order photon correlations of faint quantum light: a short review

“…Several different PDC process parameters can be used to tune the effective mode number such as the pump bandwidth [173][174][175] or its mode profile [176]. In particular systems, the number of exited modes can be engineered and a direct selection of the desired spatial or temporal modes has become possible [177][178][179][180]. Apart from that spectral filtering provides simple means for reducing the mode number of the twin beams [49].…”