Interface between picosecond and nanosecond quantum light pulses

Light is a key information carrier, enabling worldwide, high-speed data transmission through a telecommunication fibre network. This information-carrying capacity can be extended to transmitting quantum information (QI) by encoding it in single photons—flying qubits. However, the various QI-processing platforms operate at vastly different timescales. QI-processing units in atomic media, operating within nanosecond to microsecond timescales, and high-speed quantum communication, at picosecond timescales, cannot be linked efficiently because of the orders-of-magnitude mismatch in the timescales or, correspondingly, spectral linewidths. Here we develop a large-aperture time lens using wide-bandwidth electro-optic phase modulation to bridge this gap. We demonstrate coherent, deterministic spectral bandwidth compression of quantum light pulses by more than two orders of magnitude with high efficiency. This will facilitate large-scale hybrid QI-processing by linking the ultrafast and quasi-continuous-wave experimental platforms, which until now, to a large extent, have been developing independently. To bridge the ultrafast and slow classes of quantum-information-processing systems, a Fresnel time lens is developed by using a wideband electro-optic phase modulator combined with a dispersion element. The single-photon spectral bandwidth is compressed from picosecond to nanosecond timescales.