Photons are critical to quantum technologies because they can be used for virtually all quantum information tasks, for example, in quantum metrology1, as the information carrier in photonic quantum computation2, 3, as a mediator in hybrid systems4, and to establish long-distance networks5. The physical characteristics of photons in these applications differ drastically; spectral bandwidths span 12 orders of magnitude from 50 THz (ref. 6) for quantum-optical coherence tomography7 to 50 Hz for certain quantum memories8. Combining these technologies requires coherent interfaces that reversibly map centre frequencies and bandwidths of photons to avoid excessive loss. Here, we demonstrate bandwidth compression of single photons by a factor of 40 as well as tunability over a range 70 times that bandwidth via sum-frequency generation with chirped laser pulses. This constitutes a time-to-frequency interface for light capable of converting time-bin to colour entanglement9, and enables ultrafast timing measurements. It is a step towards arbitrary waveform generation10 for single and entangled photons.
a, A broad-bandwidth single photon (P) with a linear frequency chirp is converted into a narrowband photon of higher frequency via SFG with a strong laser pulse (L) of opposite chirp, in a nonlinear crystal (NL). b,
The signal photons at the source (shown in red) have an initial bandwidth of 1,740 GHz centred at 811 nm after transmission through an interference filter. Once the quadratic phase is applied and the photons are upconverted, the photon…
The centre wavelength of the upconverted light can be tuned by controlling the relative delay between the input pulses at the nonlinear crystal. The blue circles represent the centre wavelength of the upconverted single photon, spanning…
The signal and idler from SPDC are produced in pairs, strongly correlated in time with a total measured coincidence rate of 160,000 s−1 around zero delay. b, The upconverted single photon maintains the strong timing correlation expec…
