We demonstrate single-photon counting at 1550 nm with titanium-nitride (TiN) microwave kinetic inductance detectors. Energy resolution of 0.4 eV and arrival-time resolution of 1.2 microseconds are achieved. 0-, 1-, 2-photon events are resolved and shown to follow Poisson statistics. We find that the temperature-dependent frequency shift deviates from the Mattis-Bardeen theory, and the dissipation response shows a shorter decay time than the frequency response at low temperatures. We suggest that the observed anomalous electrodynamics may be related to quasiparticle traps or subgap states in the disordered TiN films. Finally, the electron density-of-states is derived from the pulse response.Fast and efficient photon-counting detectors at nearinfrared wavelengths are in high demand for advanced quantum-optics applications such as quantum key distribution[1] and linear-optics quantum computing [2]. Superconducting detectors, including superconducting nanowire detectors [3] and transition-edge sensors (TES) [4], show great promise in these applications. For example, TES made from tungsten films have shown over 95 % of quantum efficiency and photon-number resolving power at 1550 nm [5]. On the other hand, microwave kinetic inductance detectors (MKIDs) have quickly developed into another major superconducting detector technology for astronomical instruments from submillimeter to x-ray [6,7]. The main advantages of MKIDs are that they are simple to fabricate and easy to multiplex into a large detector array. Recently, the AR-CRON camera[8], a MKID array made from titanium nitride (TiN) films developed for UV/Optical/NIR imaging and spectroscopy [9], has been successfully demonstrated at the Palomar 200-inch telescope. These TiN MKIDs have already shown good photon-counting and energyresolving capability, but so far they have been considered only for astronomy applications. In this letter, we describe a single-photon-counting experiment at 1550 nm with TiN MKIDs and discuss their promise for application in quantum optics. Another motivation for the work in this letter is to use these detectors to study the electrodynamics and microwave properties of TiN, which is a relatively new material for MKIDs. Anomalous electrodynamics of TiN is discussed and the density of states * U.S. government work not protected by U.S. copyright. N 0 = 3.9 × 10 10 eV −1 µm −3 is derived. MKIDs are thin-film, high-Q superconducting microresonators whose resonance frequency f r and internal quality factor Q i (or internal dissipation) change when incoming radiation with photon energy above twice the gap energy (hν > 2∆) breaks Cooper pairs in the superconductor [6]. The measurements of frequency shift and internal dissipation signals are referred to as frequency readout and dissipation readout, respectively. The principle of operation of the MKID, as well as the readout schemes, were explained in detail in a recent review paper [10].A recent breakthrough in MKID development is the application of titanium nitride (TiN), a new material for super...

We describe a tunable-cavity quantum electrodynamics (QED) architecture with an rf SQUID phase qubit inductively coupled to a single-mode, resonant cavity with a tunable frequency that allows for both microwave readout of tunneling and dispersive measurements of the qubit. Dispersive measurement is well characterized by a three-level model, strongly dependent on qubit anharmonicity, qubit-cavity coupling, and detuning. A tunable-cavity frequency provides a way to strongly vary both the qubit-cavity detuning and coupling strength, which can reduce Purcell losses, cavity-induced dephasing of the qubit, and residual bus coupling for a system with multiple qubits. With our qubit-cavity system, we show that dynamic control over the cavity frequency enables one to avoid Purcell losses during coherent qubit evolutions and optimize state readout during qubit measurements. The maximum qubit decay time T 1 = 1.5 μs is found to be limited by surface dielectric losses from a design geometry similar to planar transmon qubits.

Signal attenuation limits the operating range in wireless communications and location. To solve the reduced range problem, we can use low-frequency signals in combination with magnetic sensing. We propose the use of an optically pumped magnetometer as a sensor and realize a proof-of-principle detection of binary phase shift keying (BPSK) modulated signals. We demonstrate a ranging enhancement by exploiting both the magnetometer's intrinsic sensitivity of below 1 pT/Hz and its 1 kHz operating bandwidth through the use of BPSK signals.

Articles you may be interested inDevelopment of magnetoresistive thin film sensor for magnetic field sensing applications AIP Conf. Proc. 1512, 30 (2013); 10.1063/1.4790897 Domain wall displacement in Py square ring for single nanometric magnetic bead detection Magnetism in zigzag-shaped thin-film elements is investigated using scanning electron microscopy with polarization analysis, magnetotransport measurements, and micromagnetic simulations. We find that the angle of magnetization alternates along the length of the element, and is strongly correlated to the corrugated edges. We show that this simple and unique geometry can be used as a single-axis magnetic field sensor. In this configuration, the sensors are primarily sensitive to fields parallel to the applied current. Our results can be interpreted in terms of a coherent rotation model of the magnetization. These devices are scalable to nanometer dimensions.

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