Christof Eigner

Highly efficient frequency conversion with bandwidth compression of quantum light

We demonstrate an engineered sum-frequency-conversion process in lithium nio-bate that provides a bandwidth compression factor of 7.47 at a high efficiency of 61.5 %, thus outperforming spectral filtering. The process preserves non-classical photon-number statistics.

Heralded generation of high-purity ultrashort single photons in programmable temporal shapes

We experimentally demonstrate a source of nearly pure single photons in arbitrary temporal shapes heralded from a parametric down-conversion (PDC) source at telecom wavelengths. The technology is enabled by the tailored dispersion of in-house fabricated waveguides with shaped pump pulses to directly generate the PDC photons in on-demand temporal shapes. We generate PDC photons in Hermite-Gauss and frequency-binned modes and confirm a minimum purity of 0.81, even for complex temporal shapes.

Fast time-domain measurements on telecom single photons

Direct measurements on the temporal envelope of quantum light are a challenging task and not many examples are known because most classical pulse characterisation methods do not work on the single-photon level. Knowledge of both spectrum and timing can, however, give insights on properties that cannot be determined by the spectral intensity alone. While temporal measurements on single photons on timescales of tens of picoseconds are possible with superconducting photon detectors, and picosecond measurements have been performed using streak cameras, there are no commercial single-photon sensitive devices with femtosecond resolution available. While time-domain sampling using sum-frequency generation has already been exploited for such a measurement, inefficient conversion has necessitated long integration times to build the temporal profile. We demonstrate a highly efficient waveguided sum-frequency generation process in Lithium Niobate to measure the temporal envelope of single photons with femtosecond resolution with short enough acquisition time to provide a live-view of the measurement. We demonstrate the measurement technique and combine it with spectral measurements using a dispersive-fibre time-of-flight spectrometer to determine upper and lower bounds for the spectral purity of heralded single photons. The approach complements the joint spectral intensity measurements as a measure on the purity can be given without knowledge of the spectral phase.

Waveguide Cavity Resonator as a Source of Optical Squeezing

We present the generation of continuous-wave optical squeezing from a titanium-indiffused lithium niobate waveguide resonator. We directly measure 2.9\pm 0.1 dB of single-mode squeezing, which equates to a produced level of 4.9\pm 0.1 dB after accounting for detection losses. This device showcases the current capabilities of this waveguide architecture and precipitates more complicated integrated continuous-wave quantum devices in the continuous-variable regime.

Fabrication of low-loss Rb-exchanged ridge waveguides in z-cut KTiOPO 4

We report on the fabrication and characterization of ridge waveguides in z-cut KTiOPO4 fabricated by Rb-ion exchange and subsequent precise diamond-blade dicing. Low attenuation values of 1.3 dB/cm (1.6 dB/cm) were determined at a wavelength of 1550 nm for TE (TM) polarization. Surface quality obtained by dicing is excellent for side walls of diced ridges and prepared end faces used for light coupling. The dispersion characteristics of the waveguides are determined and the results are compared to simulations. Finally, the nonlinear performance of the ridges is demonstrated by second harmonic generation of ∼1060 nm pump light.

A two-channel, spectrally degenerate polarization entangled source on chip

Integrated optics provides the platform for the experimental implementation of highly complex and compact circuits for quantum information applications. In this context integrated waveguide sources represent a powerful resource for the generation of quantum states of light due to their high brightness and stability. However, the confinement of the light in a single spatial mode limits the realization of multi-channel sources. Due to this challenge one of the most adopted sources in quantum information processes, i.e. a source which generates spectrally indistinguishable polarization entangled photons in two different spatial modes, has not yet been realized in a fully integrated platform. Here we overcome this limitation by suitably engineering two periodically poled waveguides and an integrated polarization splitter in lithium niobate. This source produces polarization entangled states with fidelity of

Periodically poled ridge waveguides in KTP for second harmonic generation in the UV regime

{\mathcal F} \mathrm{=0.973}\pm 0.003

Streak camera imaging of single photons at telecom wavelength

F= 0.973±0.003 and a test of Bell’s inequality results in a violation larger than 14 standard deviations. It can work both in pulsed and continuous wave regime. This device represents a new step toward the implementation of fully integrated circuits for quantum information applications.Quantum Information: the realization of integrated entangled photons sourcesIn the context of quantum technology, integrated photonic devices demonstrated great potential to perform quantum tasks stably with ease. Despite the great development of integrated circuits, the generation of quantum states of light remains challenging in an integrated geometry. In particular, one of the most adopted source in quantum information processes, the one firstly proposed by Kwiat et al. (PRL 75, 4337 1995) which provides polarization entangled photons at the same wavelength, was still not available on an integrated platform. Christine Silberhorn and co-workers from the University of Paderborn (Germany), overcome the previous technological issues and realized such a quantum source. With this achievement the Authors provide a device that performs better than the corresponding bulk schemes and is an optimal candidate to be exploited with integrated linear circuit for a full generation and manipulation of polarization encoded qubits in integrated platforms.