We demonstrate photon-noise limited performance at sub-millimeter wavelengths in feedhorn-coupled, microwave kinetic inductance detectors (MKIDs) made of a TiN/Ti/TiN trilayer superconducting film, tuned to have a transition temperature of 1.4 K. Micro-machining of the silicon-on-insulator wafer backside creates a quarter-wavelength backshort optimized for efficient coupling at 250 µm. Using frequency read out and when viewing a variable temperature blackbody source, we measure device noise consistent with photon noise when the incident optical power is > 0.5 pW, corresponding to noise equivalent powers > 3×10 −17 W/ √ Hz. This sensitivity makes these devices suitable for broadband photometric applications at these wavelengths.

Microwave resonances between discrete macroscopically distinct quantum states with single photon and multiphoton absorption are observed in a strongly driven radio frequency superconducting quantum interference device flux qubit. The amplitude of the resonant peaks and dips are modulated by the power of the applied microwave irradiation and a population inversion is generated at low flux bias. These results, which can be addressed with Landau-Zener transition, are useful to develop an alternative means to initialize and manipulate the flux qubit, as well as to do a controllable population inversion used in a micromaser. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3093823͔As controllable artificial atoms, superconducting qubits have received considerable attention because of providing a new paradigm of quantum solid state physics. So far, many fantastic macroscopic quantum coherent phenomena 1,2 have been demonstrated in superconducting qubits. In addition, recent experiments show that the interaction between superconducting qubits and microwave ͑MW͒ resonant cavity can produce single photon, 2 which leads to a possible application of superconducting qubits as a micromaser. It is well known that population inversion, which maintains a majority of atoms in excited states rather than in ground state, has to be realized in order to ensure the amplification of the light and thus the laser process. Previous work 3,4 suggests that it is possible to generate population inversion in the superconducting quantum circuits subjected to MW radiation. In this letter, we report a further step in this direction: a controllable population inversion in a strongly driven radio frequency superconducting quantum interference device ͑rf-SQUID͒ by employing Landau-Zener ͑LZ͒ transition.LZ transition is a celebrated quantum mechanical phenomenon in the quantum world.5-7 It has been found in various physical systems, such as atoms in accelerating optical lattices, 8,9 superlattices, 10 nanomagnets, 11,12 quantum dots, 13 and Josephson junctions. [14][15][16] Recently LZ transition is also found in the superconducting qubits, [17][18][19][20] providing new insights into the fundamentals of quantum mechanics and holding promise for the superconducting qubits' application. One may use LZ to enhance the quantum tunneling rate, 21,22 prepare the quantum state, 23 control the qubit gate operations 13,24 effectively, and do the controllable population inversion as demonstrated in this letter.Our design of the superconducting flux qubit, being immune to charge noise and comparatively easy to be read out, is based on rf-SQUID. 25 An rf-SQUID consists of a superconducting loop with inductance L interrupted by one Josephson junction with capacitance C and critical current I c . Its dynamics can be described in terms of the variable ⌽ and are identical to those of a particle of "mass" C with kinetic energy C⌽ 2 / 2 moving in the potential U͑⌽͒. Herewhere ⌽ 0 is the flux quantum,close to one half of a flux quantum is applied, the potential ...

We demonstrate photon counting at 1550 nm wavelength using microwave kinetic inductance detectors (MKIDs) made from TiN/Ti/TiN trilayer films with superconducting transition temperature Tc ≈ 1.4 K. The detectors have a lumped-element design with a large interdigitated capacitor covered by aluminum and inductive photon absorbers whose volume ranges from 0.4 µm 3 to 20 µm 3 . The energy resolution improves as the absorber volume is reduced. We achieved an energy resolution of 0.22 eV and resolved up to 7 photons per optical pulse, both greatly improved from previously reported results at 1550 nm wavelength using MKIDs. Further improvements are possible by optimizing the optical coupling to maximize photon absorption into the inductive absorber.Photon-number-resolving (PNR) detectors at near infrared wavelengths have important applications in a number of frontier fields, such as quantum secure communications [1], linear optical quantum computing [2] and optical quantum metrology [3]. Compared to more conventional detectors at this wavelength, such as siliconbased detectors [4], superconducting detectors have lower dark-count rate, higher sensitivity, and broadband response. They show great promise in serving as the basic building blocks for efficient PNR devices. For example, by spatial or temporal multiplexing of superconducting nanowire single-photon detectors (SNSPDs) [5][6][7][8], photons can be counted at high speed. But the singleelement nanowire has no intrinsic PNR and energyresolving capabilities. Alternatively, single-element transition edge sensors (TESs) [9] have demonstrated high quantum efficiency and multi-photon discrimination at telecommunication wavelengths [10][11][12]. Recently, counting up to 29 photons and intrinsic energy resolution ≈ 0.11 eV at 1550 nm wavelength have been achieved in Ti/Au TESs [13][14][15].Another type of superconducting detector possessing intrinsic photon-number-resolving and energy-resolving power is the microwave kinetic inductance detector (MKID) [16]. MKIDs are cooper pair breaking detectors based on high-quality factor (high-Q) superconducting resonators [17,18]. The absorption of a photon with energy higher than twice the gap energy (hν > 2∆) can break Cooper pairs into quasiparticles, changing the surface impedance of the resonator and resulting in a lower resonance frequency f r and higher internal dissipation (or lower quality factor Q i ). When applying a short optical pulse to the detector and probing the resonator with a * Electronic mail: qubit@home.swjtu.edu.cn † Electronic mail: weilianfu@gmail.com ‡ Contribution of the U.S. government, not subject to copyright microwave tone near the resonance frequency, one can obtain a pulse response in the complex forward transmission S 21 , as shown in Fig. 1(a). This photon response can be measured using a homodyne detection scheme ( Fig. 1(d)) and the signal can be decomposed into frequency and dissipation responses ( Fig. 1(a),(b)) for pulse analysis. Compared to TESs, MKIDs are easy to fabricate and multiplex into...

Total syntheses of multidrug resistant inhibitors (-)-acetylardeemin 2a, (-)-ardeemin 2b, and (-)-formylardeemin 3 have been achieved within 10 steps starting from bromopyrroloinoline 13. The key step involves direct alkylation of 13 with prenyl tributylstannane 11 to yield 12 via a silver-promoted asymmetric Friedel-Crafts reaction. Highly efficient installation of the isoprenyl group allowed excellent overall yield. Moreover, the substrate scope of the asymmetric Friedel-Crafts reaction of 13 was expanded to include a variety of arenes 14 to afford natural product-like library analogues 15.

Proton exchanged channel waveguides in x-cut single-crystal lithium niobate thin film could avoid optical leakage loss which existed in the z-cut case. Indicated by simulations, the mechanism and condition of the optical leakage loss were studied. The light energy in the exchanged layer and the mode sizes were calculated to optimize the parameters for fabrication. By a very short time (3 minutes) proton exchange process without anneal, the channel waveguide with 2 μm width and 0.16 μm exchanged depth in the x-cut lithium niobate thin film had a propagation loss as low as 0.2 dB/cm at 1.55 μm. Furthermore, the Y-junctions based on the low-loss waveguide were designed and fabricated. For a Y-junction based on the 3 μm wide channel waveguide with 8000 μm bending radius, the total transmission could reach 85% ~90% and the splitting ratio maintained at a stable level around 1:1. The total length was smaller than 1 mm, much shorter than the conventional Ti-diffused and proton exchanged Y-junctions in bulk lithium niobate.

A microwave superconducting quantum interference device multiplexer has been optimized for reading out large arrays of superconducting transition-edge sensor (TES) bolometers. We present the scalable cryogenic multiplexer chip design that may be used to construct an 1820-channel multiplexer for the 4–8 GHz rf band. The key metrics of yield, sensitivity, and crosstalk are determined through measurements of 455 readout channels, which span 4–5 GHz. The median white-noise level is 45 pA/Hz, evaluated at 2 Hz, with a 1/f knee ≤ 20 mHz after common-mode subtraction. The white-noise level decreases the sensitivity of a TES bolometer optimized for detection of the cosmic microwave background at 150 GHz by only 3%. The measured crosstalk between any channel pair is ≤ 0.3%.

We present a wafer trimming technique for producing superconducting micro-resonator arrays with highly uniform frequency spacing. With the light-emitting diode (LED) mapper technique demonstrated previously, we first map the measured resonance frequencies to the physical resonators. Then, we fine-tune each resonator's frequency by lithographically trimming a small length, calculated from the deviation of the measured frequency from its design value, from the interdigitated capacitor. We demonstrate this technique on a 127-resonator array made of titanium-nitride (TiN) and show that the uniformity of frequency spacing is greatly improved. The array yield in terms of frequency collisions improves from 84 % to 97 %, while the quality factors and noise properties are unaffected. The wafer trimming technique provides an easy-to-implement tool to improve the yield and multiplexing density of large resonator arrays, which is important for various applications in photon detection and quantum computing.

We report low-loss channel waveguides in a single-crystal LiNbO(3) thin film achieved using the annealed proton exchange process. The simulation indicated that the mode size of the α phase channel waveguide could be as small as 1.2  μm(2). Waveguides with several different widths were fabricated, and the 4 μm-wide channel waveguide exhibited a mode size of 4.6  μm(2). Its propagation loss was accurately evaluated to be as low as 0.6 dB/cm at 1.55 μm. The single-crystal lattice structure in the LiNbO(3) thin film was preserved by a moderate annealed proton exchange process (5 min of proton exchange at 200°C, followed by 3 h annealing at 350°C), as revealed by measuring the extraordinary refractive index change and x ray rocking curve. A longer proton exchange time followed by stronger annealing would destroy the crystal structure and induce a high loss in the channel waveguides.