The quantum Rabi model describing the fundamental interaction between light and matter is a cornerstone of quantum physics. It predicts exotic phenomena like quantum phase transitions and ground-state entanglement in ultrastrong and deep-strong coupling regimes, where coupling strengths are comparable to or larger than subsystem energies. Demonstrating dynamics remains an outstanding challenge, the few experiments reaching these regimes being limited to spectroscopy. Here, we employ a circuit quantum electrodynamics chip with moderate coupling between a resonator and transmon qubit to realise accurate digital quantum simulation of deep-strong coupling dynamics. We advance the state of the art in solid-state digital quantum simulation by using up to 90 second-order Trotter steps and probing both subsystems in a combined Hilbert space dimension of ∼80, demonstrating characteristic Schrödinger-cat-like entanglement and large photon build-up. Our approach will enable exploration of extreme coupling regimes and quantum phase transitions, and demonstrates a clear first step towards larger complexities such as in the Dicke model.
In tokamak plasmas with a tearing mode, strong scattering of high power millimeter waves, as used for heating and noninductive current drive, is shown to occur. This new wave scattering phenomenon is shown to be related to the passage of the O point of a magnetic island through the high power heating beam. The density determines the detailed phasing of the scattered radiation relative to the O-point passage. The scattering power depends strongly nonlinearly on the heating beam power.
Aims. Future astrophysics and cosmic microwave background space missions operating in the far-infrared to millimetre part of the spectrum will require very large arrays of ultra-sensitive detectors in combination with high multiplexing factors and efficient lownoise and low-power readout systems. We have developed a demonstrator system suitable for such applications. Methods. The system combines a 961 pixel imaging array based upon Microwave Kinetic Inductance Detectors (MKIDs) with a readout system capable of reading out all pixels simultaneously with only one readout cable pair and a single cryogenic amplifier. We evaluate, in a representative environment, the system performance in terms of sensitivity, dynamic range, optical efficiency, cosmic ray rejection, pixel-pixel crosstalk and overall yield at an observation centre frequency of 850 GHz and 20% fractional bandwidth. Results. The overall system has an excellent sensitivity, with an average detector sensitivity NEP det = 3 × 10 −19 W/ √ Hz measured using a thermal calibration source. At a loading power per pixel of 50 fW we demonstrate white, photon noise limited detector noise down to 300 mHz. The dynamic range would allow the detection of ∼1 Jy bright sources within the field of view without tuning the readout of the detectors. The expected dead time due to cosmic ray interactions, when operated in an L2 or a similar far-Earth orbit, is found to be <4%. Additionally, the achieved pixel yield is 83% and the crosstalk between the pixels is <−30 dB. Conclusions. This demonstrates that MKID technology can provide multiplexing ratios on the order of a 1000 with state-of-the-art single pixel performance, and that the technology is now mature enough to be considered for future space based observatories and experiments.
We study spin relaxation and diffusion in an electron-spin ensemble of nitrogen impurities in diamond at low temperature (0.25-1.2 K) and polarizing magnetic field (80-300 mT). Measurements exploit mode-and temperature-dependent coupling of hyperfine-split sub-ensembles to the resonator. Temperature-independent spin linewidth and relaxation time suggest that spin diffusion limits spin relaxation. Depolarization of one sub-ensemble by resonant pumping of another indicates fast cross-relaxation compared to spin diffusion, with implications on use of sub-ensembles as independent quantum memories.PACS numbers: 42.50.Pq, 03.67.Lx The study of spin ensembles coupled to superconducting integrated circuits is of both technological and fundamental interest. An eventual quantum computer may involve a hybrid architecture [1-4] combining superconducting qubits for processing of information, solid-state spins for storage, and superconducting resonators for interconversion. Additionally, superconducting resonators allow the study of spin ensembles at low temperatures with ultra-low excitation powers and high spectral resolution [5,6]. While one spin couples to one microwave photon with strength g/2π ∼ 10 Hz, an ensemble of N spins collectively couples with g ens = g √ N [7,8], reaching the strong-coupling regime g ens > κ, γ at N 10 12 [8][9][10], where κ and γ are the circuit damping and spin dephasing rates, respectively.Among the solid-state spin ensembles under consideration, nitrogen defects in diamond (P1 centers) [11] are excellent candidates for quantum information processing. Diamond samples can be synthesized with P1 centers as only paramagnetic impurities. Additionally, samples with spin densities ranging from highly dense (> 200 ppm) to very dilute (< 5 ppb) are commercially available, allowing the tailoring of spin linewidth (γ ∝ N [12]) and collective strength (g ens ∝ √ N ). In contrast to nitrogen-vacancy centers in diamond [13] and rare-earth ions in Y 2 SiO 5 [14, 15], P1 centers are optically inactive, making a coupled microwave resonator an ideal probe for their study. However, the magnetic fields 100 mT needed to polarize the ensemble at the few-GHz transition frequencies of circuits [16] must not compromise superconductivity. The freezing of all spin dynamics in a high-purity P1 ensemble by the field would allow quenching spin decoherence [17] through dynamical decoupling [18], realizing a useful quantum memory. * These authors contributed equally to this work.Here, we investigate the dynamics of a P1 electron-spin ensemble probed by controlled coupling to two modes of a coplanar waveguide (CPW) resonator. The resonator is patterned on a NbTiN film [19] withstanding applied magnetic fields beyond 300 mT. Three hyperfine-split spin sub-ensembles are clearly resolved over the temperature range 0.25-1.2 K. The collective coupling of each arXiv:1208.5473v1 [cond-mat.mes-hall]
Terahertz spectrometers with a wide instantaneous frequency coverage for passive remote sensing are enormously attractive for many terahertz applications, such as astronomy, atmospheric science and security. Here we demonstrate a wide-band terahertz spectrometer based on a single superconducting chip. The chip consists of an antenna coupled to a transmission line filterbank, with a microwave kinetic inductance detector behind each filter. Using frequency division multiplexing, all detectors are read-out simultaneously creating a wide-band spectrometer with an instantaneous bandwidth of 45 GHz centered around 350 GHz. The spectrometer has a spectral resolution of F/∆F = 380 and reaches photon-noise limited sensitivity. We discuss the chip design and fabrication, as well as the system integration and testing. We confirm full system operation by the detection of an emission line spectrum of methanol gas. The proposed concept allows for spectroscopic radiation detection over large bandwidths and resolutions up to F/∆F ∼ 1000, all using a chip area of a few cm 2 . This will allow the construction of medium resolution imaging spectrometers with unprecedented speed and sensitivity.
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