The practical prospect of quantum communication and information processing relies on sophisticated single photon pairs which feature controllable waveform, narrow spectrum, excellent purity, fiber compatibility and miniaturized design. For practical realizations, stable, miniaturized, low-cost devices are required.Sources with one or some of above performances have been demonstrated already, but it is quite challenging to have a source with all of the described characteristics simultaneously. Here we report on an integrated singlelongitudinal-mode non-degenerate narrowband photon pair source, which exhibits all requirements needed for quantum applications. The device is composed of a periodically poled Ti-indiffused lithium niobate waveguide with high reflective dielectric mirror coatings deposited on the waveguide end-faces. Photon pairs with wavelengths around 890 nm and 1320 nm are generated via type II phasematched parametric down-conversion. Clustering in this dispersive cavity restricts the whole conversion spectrum to one single-longitudinal-mode in a single cluster yielding a narrow bandwidth of only 60 MHz. The high conversion efficiency in the waveguide, together with the spectral clustering in the doubly resonant waveguide, leads to a high brightness of 3 × 10 4 pairs/(s•mW•MHz). This source exhibits prominent single-longitudinal-mode purity and remarkable temporal shaping capability. Especially, due to temporal broadening, we can observe that the coherence time of the two-photon component of PDC state is actually longer than the one of the single photon states. The miniaturized monolithic design makes this source have various fiber communication applications.

An integrated chip with quantum state generation, active polarization manipulation, and precise time control is demonstrated.

We report on the implementation of quantum frequency conversion (QFC) between infrared (IR) and ultraviolet (UV) wavelengths by using single-stage upconversion in a periodically poled KTP waveguide. Due to the monolithic waveguide design, we manage to transfer a telecommunication band input photon to the wavelength of the ionic dipole transition of Yb + at 369.5 nm. The external (internal) conversion efficiency is around 5% (10%). The high energy pump used in this converter introduces a spontaneous parametric downconversion (SPDC) process, which is a cause for noise in the UV mode. Using this SPDC process, we show that the converter preserves non-classical correlations in the upconversion process, rendering this miniaturized interface a source for quantum states of light in the UV.Quantum networks and long distance quantum communication rely on the faithful transfer and manipulation of quantum states. Because a single quantum system does not necessarily incorporate all the benefits needed, a hybrid system [1, 2] with different nodes operating at dissimilar frequencies may be used to perform each task at its optimal frequency. The process of quantum frequency conversion (QFC) [3,4] has been established as a means to bridge the gap between differing frequencies while keeping the quantum correlations intact. On the one side of that gap, telecommunications bands in the infrared spectral region have consensually been identified as the optimal wavelengths for quantum state transfer because of low loss in optical fibers and a multitude of experimental studies have shown QFC from [4][5][6][7][8][9][10][11] and to [12][13][14][15][16][17] the telecommunications bands, c.f. Fig. 1 (a). Looking at the other side of the gap, one finds that QFC experiments have so far mainly focused on convenient laser wavelengths or transitions in the red/near-infrared spectral region. However, high fidelity photonic state manipulation strongly benefits from high energy transitions and indeed, most of the beneficial ionic transitions are situated at ultraviolet (UV) wavelengths. Most prominently, the Ytterbium-(Yb + ) transition at 369.5 nm constitutes an almost ideal 2-level quantum system due to the Yb + -ion's specific electronic structure [18]. It has been shown that the S 1/2 → P 1/2 transition can act as a photonic interface for efficient and long lived storage of quantum bits [19], and the Yb-ion proves to be useful for quantum computing [18,20] and fundamental studies of light-matter interactions [21]. While this ion is thus an ideal system for the manipulation of quantum states, its application for quantum networks and long distance quantum communication in a hybrid system is conditioned on the possibility to connect it to the optimal fiber transmission window (c.f. fiber attenuation in Fig. 1 (c)). This is a challenging venture and involves significant engineering efforts because of the large energy gap between in-and output, as well as the properties of nonlinear materials at UV wavelengths. In contrast to a [3-10, 12-17, 24-29]...

We propose and characterize a quantum interface between telecommunication wavelengths (1311 nm) and an Yb + -dipole transition (369.5 nm) based on a second order sum frequency process in a PPKTP waveguide. An external (internal) conversion efficiency above 5% (10%) is shown using classical bright light.

We demonstrate an approach to all-optical switching, where a weak beam controls a strong beam, based on three-wave mixing optical parametric amplification in a nonlinear crystal. Ultrafast switching within 400fs has been achieved with a 130fs single-photon level switch beam containing, on average, 0.75 photon/pulse, which can turn on/off a signal pulse containing 5.9×108 photons. The transverse patterns for the on and off states are well defined and the switch has a large bandwidth of up to 10nm.