The ability to generate single photons is not only an ubiquitous tool for scientific exploration with applications ranging from spectroscopy and metrology 1,2 to quantum computing 3 , but also an important proof of the underlying quantum nature of a physical process 4 . In the microwave regime, emission of anti-bunched radiation has so far relied on coherent control of Josephson qubits 5-8 , where precisely calibrated microwave pulses are needed, and the achievable bandwidth is limited by the anharmonicity of the qubit. Here, we demonstrate the operation of a bright on-demand source of quantum microwave radiation capable of emitting anti-bunched photons based on inelastic Cooper pair tunneling and driven by a simple DC voltage bias. It is characterized by its normalized second order correlation function of g (2) (0) ≈ 0.43 corresponding to anti-bunching in the single photon regime. Our source can be triggered and its emission rate is tunable in situ exceeding rates obtained with current microwave single photon sources by more than one order of magnitude.

Niobium nitride (NbN) is widely used in high-frequency superconducting electronics circuits because it has one of the highest superconducting transition temperatures (Tc ∼ 16.5 K) and largest gap among conventional superconductors. In its thin-film form, the Tc of NbN is very sensitive to growth conditions and it still remains a challenge to grow NbN thin film (below 50 nm) with high Tc. Here, we report on the superconducting properties of NbN thin films grown by high-temperature chemical vapor deposition (HTCVD). Transport measurements reveal significantly lower disorder than previously reported, characterized by a Ioffe-Regel (kF ℓ) parameter of ∼ 14. Accordingly we observe Tc ∼ 17.06 K (point of 50 % of normal state resistance), the highest value reported so far for films of thickness below 50 nm, indicating that HTCVD could be particularly useful for growing high quality NbN thin films.Niobium nitride (NbN)thin films -thanks to their high T c ∼ 16.5 K, superconducting energy gap ∆ ∼ 2.5 meV, and upper critical field B c2 ∼ 40 T -have been the subject of intense research for the last few decades, both on application and fundamental grounds. The combination of high T c and small coherence length (ξ(0) ∼ 5 nm) allows one to fabricate very thin NbN films with reasonably high T c , which is essential for, e.g, Superconducting Single Photon Detectors (see e.g. [1,2]). NbN thin films are used as hot electron bolometers and superconducting radio frequency cavities. NbN has higher kinetic inductance to other S-wave superconductors [3], which this helps fabricating superconducting micro wave resonators with high characteristic impedance and microwave kinetic inductance detectors. On the fundamental level, the effects of disorder on superconducting and normal state properties have been studied in NbN thin films [4][5][6]. Nano-wires, made from NbN thin films, have demonstrated thermal and quantum phase slips [7]a phenomenon of great interest in understanding onedimensional superconductivity. Further, the large superconducting energy gap of NbN can be explored in designing circuit Quantum Electrodynamics experiments in the THz frequency range.Thus, there has been a growing demand of high quality NbN thin films. Reactive DC magnetron sputtering from an Nb target in an argon and nitrogen atmosphere is most commonly used to deposit NbN on various substrates [8][9][10]. The main difficulty in this process, arises from the creation of atomic level nitrogen vacancies and from the formation of non-superconducting Nb 2 N and hexagonal phases. Besides, in the optimal parameter range, the high sputtering rate (typically ∼ 1-5 nm/sec) makes it difficult to control the thickness below 10 nm. Some other methods, where the superconducting properties of NbN thin films were probed, include Pulsed Laser Deposition (PLD) [11,12], Molecular Beam Epitaxy (MBE) [13] and Atomic Layer Deposition (ALD) [14]. In this regard, de-position of superconducting NbN films by high temperature chemical vapor deposition (HTCVD) is rather rare. HTCVD, comp...

The interaction between propagating microwave fields and Cooper-pair tunneling across a DC voltage-biased Josephson junction can be highly nonlinear. We show theoretically that this nonlinearity can be used to convert an incoming single microwave photon into an outgoing n-photon Fock state in a different mode. In this process, the electrostatic energy released in a Cooper-pair tunneling event is transferred to the outgoing Fock state, providing energy gain. The created multi-photon Fock state is frequency entangled and highly bunched. The conversion can be made reflectionless (impedance-matched) so that all incoming photons are converted to n-photon states. With realistic parameters multiplication ratios n > 2 can be reached. By two consecutive multiplications, the outgoing Fock-state number can get sufficiently large to accurately discriminate it from vacuum with linear post-amplification and power measurement. Therefore, this amplification scheme can be used as single-photon detector without dead time. PACS numbers: 42.65.-k, 74.50.+r, 85.25.Cp, 85.60.Gzexhibits the strong nonlinearity of this light-charge interaction most clearly, due to the absence of quasi-particle excitations. This system is understood to be a bright and robust on-chip source of nonclassical microwave radiation, such as of antibunched photons [34,35], nonclassical photon pairs [24,28,31,36], and multi-photon Fock states [40,41].We explore theoretically a process which converts a propagating photon in one mode to n photons in another arXiv:1612.07098v2 [cond-mat.mes-hall] 1 Feb 2018where the Josephson in-Hamiltonian has the formand the Josephson out-HamiltonianThe two Josephson frequencies account for different voltage biases of the islands, ω in J = 2eV in and ω out J = 2eV out . The free evolution resonator Hamiltonian is now

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Nature sets fundamental limits regarding how accurate the amplification of analog signals may be. For instance, a linear amplifier unavoidably adds some noise which amounts to half a photon at best. While for most applications much higher noise levels are acceptable, the readout of microwave quantum systems, such as spin or superconducting qubits, requires noise as close as possible to this ultimate limit. To date, it is approached only by parametric amplifiers exploiting non-linearities in superconducting circuits and driven by a strong microwave pump tone. However, this microwave drive makes them much more difficult to implement and operate than conventional DC powered amplifiers, which so far suffer from much higher noise. Here we present the first experimental proof that a simple DC-powered setup allows for amplification close to the quantum limit. Our amplification scheme is based on the stimulated microwave photon emission accompanying inelastic Cooper pair tunneling through a DC-biased Josephson junction, with the key to low noise lying in a well defined auxiliary idler mode, in analogy to parametric amplifiers.The quantum limit on the noise of a linear amplifier can be derived from first principles [1]. This derivation shows that in order to be amplified irrespectively of its phase, the signal necessarily has to be coupled to at least one complementary mode, called idler, and that the photon noise of this mode is added to the signal. In the ideal case, where the idler mode is in its quantum ground state and the gain is large, the added input noise is half a photon. This limit is reached by Josephson parametric amplifiers (JPAs) [2][3][4][5][6][7][8], where the nonlinear inductance of Josephson junctions is used to couple a microwave pump tone to the signal mode. They have a perfectly well defined idler mode at the frequency f i , the difference of (a multiple of) the pump frequency and the signal frequency. This frequency can be matched to a dedicated mode in the circuit which can then be put in its ground state by strongly coupling it to a dedicated cold dissipator with temperature T hf i /k B .In DC-powered amplifiers, on the other hand, this idler mode is usually not well identified and difficult to engineer. For example, in high electron mobility transistor VNA RF DC 20dB 30dB 50 Ω 10 MΩ 50 Ω

We present a new process for fabricating vertical NbN-MgO-NbN Josephson junctions using self-aligned silicon nitride spacers. It allows for a wide range of junction areas from 0.02 µm 2 to several 100 µm 2 . At the same time, it is suited for the implementation of complex microwave circuits with transmission line impedances ranging from < 1 Ω to > 1 kΩ. The constituent thin films and the finished junctions are characterized. The latter are shown to have high gap voltages (> 4 mV) and low sub-gap leakage currents.

We present an efficient fabrication method for absorptive microwave filters based on Eccosorb CR-124. Filters are fabricated from readily available parts, and their cutoff frequency can be set by their length. They exhibit desirable properties such as a very large and deep stop band with rejection beyond 120 dB at least up to 40 GHz, more than 10 dB return loss in both the pass and the stop band, and an error-function shaped step response without overshoot. Measurements at very low temperatures show that the filters thermalize on a time scale of approximately 100 s, and that they can absorb power as high as 100 nW with their noise temperature staying remarkably low, below 100 mK. These properties make the filters ideal for cryogenic filtering and filtering of intermediate frequency port signals of mixers.

RESUMOEntre as práticas de manejo recomendadas para o controle da sarna da macieira (Venturia inaequalis), o uso de cultivares geneticamente resistentes assume grande importância em programa de manejo integrado, em que a restrição ao uso de fungicidas é comum. No presente estudo utilizaram-se técnicas de análise multivariada, com o objetivo de selecionar variáveis úteis nos programas de melhoramento e na classificação de cultivares de macieira quanto à resistência parcial a V. inaequalis. Dez cultivares originárias de material propagativo de plantas com idade entre 35 e 50 anos foram avaliadas. As cultivares CNPUV-09 e CNPUV-04 apresentaram nível de resistência similar à da cultivar Prima, padrão de resistência ao patógeno. A formação de estroma + apressório (ST + AP) e a esporulação (ESP) do patógeno após a inoculação com conídios em folhas das cultivares constituíram os maiores autovetores dos dois primeiros componentes principais e contribuíram com 23,9% e 28,5% da variância total, respectivamente. SP + AP e ESP apresentaram alta correlação com os eixos dos componentes principais. Essas variáveis podem ser úteis em programas de melhoramento de macieira para a seleção de cultivares com resistência parcial a V. inaequalis. Palavras-chave: Análise de agrupamento, esporulação, estruturas de infecção, ordenação. ABSTRACT Partial resistance of old apple cultivars to Venturia inaequalisAmong the practices recommended for apple scab (Venturia inaequalis) control, the use of genetically resistant cultivars is of great importance in integrated management programs, in which restrictions to fungicide use are common. In this study we used multivariate analysis techniques to identify variables useful in apple breeding programs for detecting partial resistance to V. inaequalis and to rank cultivars for this resistance type. A collection of ten old apple cultivars from propagative material 35 to 50 years old was evaluated for partial resistance to the pathogen. CNPUV-09 and CNPUV-04 had levels of resistance similar to that of cultivar Prima, the standard resistant cultivar. The stroma and apressorium (ST + AP) formation and sporulation (ESP) of the pathogen after a foliar inoculation by conidial suspension were the largest eigenvectors of the first and second principal components, and contributed with 23.9% and 28.5% of the total variance, respectively. ST + AP and ESP were highly correlated with first and second axes. These variables could be useful in apple breeding programs to select cultivars with partial resistance to V. inaequalis. Key words: Cluster analysis, infection structures, ordination, sporulation.A sarna da macieira, causada pelo fungo ascomicota Venturia inaequalis (Cooke) G. Wint. é um dos fatores limitantes ao cultivo de macieira (Malus domestica Borkh.) nas principais regiões produtoras do mundo, incluindo o Brasil. O fungo pode atacar folhas, flores, ramos e frutos, e a doença pode reduzir a produtividade dos pomares e a qualidade dos frutos em até 100%, se não controlada (MacHardy et al., 2001).O control...