Quantum communication protocols based on nonclassical correlations can be more efficient than known classical methods and offer intrinsic security over direct state transfer. In particular, remote state preparation aims at the creation of a desired and known quantum state at a remote location using classical communication and quantum entanglement. We present an experimental realization of deterministic continuous-variable remote state preparation in the microwave regime over a distance of 35 cm. By employing propagating two-mode squeezed microwave states and feedforward, we achieve the remote preparation of squeezed states with up to 1.6 dB of squeezing below the vacuum level. Finally, security of remote state preparation is investigated by using the concept of the one-time pad and measuring the von Neumann entropies. We find nearly identical values for the entropy of the remotely prepared state and the respective conditional entropy given the classically communicated information and, thus, demonstrate close-to-perfect security.

Displacement of propagating quantum states of light is a fundamental operation for quantum communication. It enables fundamental studies on macroscopic quantum coherence and plays an important role in quantum teleportation protocols with continuous variables. In our experiments, we have successfully implemented this operation for propagating squeezed microwave states. We demonstrate that, even for strong displacement amplitudes, there is no degradation of the squeezing level in the reconstructed quantum states. Furthermore, we confirm that path entanglement generated by using displaced squeezed states remains constant over a wide range of the displacement power.

The spray-deposition technique is an effective and scalable method to deposit zinc oxide nanostructures, which are used as active layers for dye-sensitized solar cells (DSSCs) in the present study. The dynamics of structural evolution are studied with grazing incidence small-angle X-ray scattering during in situ spraying. Nanostructured films obtained through multiple spray shots provide suitable structural length scales, morphologies, and film thicknesses; this leads to reasonable performance in a DSSC with the highest short-circuit current density reported so far.

In experiments with superconducting quantum circuits, characterizing the photon statistics of propagating microwave fields is a fundamental task. We quantify the n 2 + n photon number variance of thermal microwave photons emitted from a black-body radiator for mean photon numbers 0.05 n 1.5. We probe the fields using either correlation measurements or a transmon qubit coupled to a microwave resonator. Our experiments provide a precise quantitative characterization of weak microwave states and information on the noise emitted by a Josephson parametric amplifier.As propagating electromagnetic fields in general [1][2][3], propagating microwaves with photon numbers on the order of unity are essential for quantum computation [4,5], communication [6], and illumination [7][8][9][10] protocols. Because of their omnipresence in experimental setups, the characterization of thermal states is especially relevant for many applications [11][12][13][14]. Specifically in the microwave regime, sophisticated experimental techniques for their generation at cryogenic temperatures, their manipulation, and detection have been developed in recent years. In this context, an important aspect is the generation of propagating thermal microwaves using thermal emitters [15][16][17]. These emitters can be spatially separated from the setup components used for manipulation and detection [18,19], which allows one to individually control the emitter and the setup temperature. Due to the low energy of microwave photons, the detection of these fields typically requires the use of nearquantum-limited amplifiers [20][21][22][23], cross-correlation detectors [17, 18, 24], or superconducting qubits [25][26][27][28].The unique nature of propagating fields is reflected in their photon statistics, which is described by a probability distribution either in terms of the number states or in terms of its moments. The former were studied by coupling the field to an atom or qubit and measuring the coherent dynamics [29][30][31] or by spectroscopic analysis [32]. The moment-based approach requires knowledge on the average photon number n and its variance Var(n) = n 2 − n 2 to distinguish many states of interest. To this end, the second-order correlation function g (2) (τ ) has been measured to analyze the photon statistics of thermal [33][34][35] or quantum [36][37][38] emitters ever since the ground-breaking experiments of Hanbury Brown and Twiss [39,40]. While these experiments use the time delay τ as control parameter, at microwave frequencies the photon number n can be controlled conveniently [15,32,[41][42][43][44]. In the specific case of a thermal field at frequency ω, the Bose-Einstein distribution yields n(T ) = [exp( ω/k B T ) − 1] −1 and Var(n) = n 2 + n, which can be controlled by the temperature T of the emitter. In practice, one wants to distinguish this relation from both the classical limit Var(n) = n 2 and the Poissonian behavior Var(n) = n characteristic for coherent states [41] or shot noise [45,46]. Hence, as shown in Fig. 1, the most relev...