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Schrödinger cat states, quantum superpositions of macroscopically distinct classical states, are an important resource for quantum communication, quantum metrology and quantum computation. Especially, cat states in a phase space protected against phase-flip errors can be used as a logical qubit. However, cat states, normally generated in three-dimensional cavities and/or strong multi-photon drives, are facing the challenges of scalability and controllability. Here, we present a strategy to generate and preserve cat states in a coplanar superconducting circuit by the fast modulation of Kerr nonlinearity. At the Kerr-free work point, our cat states are passively preserved due to the vanishing Kerr effect. We are able to prepare a 2-component cat state in our chip-based device with a fidelity reaching 89.1% under a 96 ns gate time. Our scheme shows an excellent route to constructing a chip-based bosonic quantum processor. Schrodinger’s cat states constitute an important resource for quantum information processing, but present challenges in terms of scalabilty and controllability. Here, the authors exploit fast Kerr nonlinearity modulation to generate and store cat states in superconducting circuits in a more scalable way.

Polycrystalline samples of Ca3−xBixCo4O9+δ (x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.30) have been prepared by conventional solid-state synthesis. Thermopower of all the samples is positive, indicating that the predominant carriers are holes over the entire temperature range. The resistivity of all the samples, except the one with x = 0.30, exhibits nonmetal to metal transition (TMI) in the low temperature regime. The resistivity results indicate that all the doped samples obey the variable range hopping in the low temperature regime. The TMI and T* (transition temperature from Fermi liquid metal to incoherent metal) increase, and the slope of A value (Fermi-liquid transport coefficient) decreases with the increasing Bi content due to an increase in chemical pressure in the lattice. Among the samples, Ca2.7Bi0.3Co4O9+δ has the highest dimensionless figure of merit of 0.091 at 300 K. This value represents an improvement of about 135 % compared to the undoped Ca3Co4O9+δ. Magnetic measurements indicate that all the samples exhibit a low-spin state of cobalt ion. The ferrimagnetic transition temperature is suppressed by the Bi dopant. These results suggest that Bi is an effective doping element for improving the thermoelectric properties of Ca3Co4O9+δ.

The parametric phase-locked oscillator (PPLO) is a class of frequency-conversion device, originally based on a nonlinear element such as a ferrite ring, that served as a fundamental logic element for digital computers more than 50 years ago. Although it has long since been overtaken by the transistor, there have been numerous efforts more recently to realize PPLOs in different physical systems such as optical photons, trapped atoms, and electromechanical resonators. This renewed interest is based not only on the fundamental physics of nonlinear systems, but also on the realization of new, high-performance computing devices with unprecedented capabilities. Here we realize a PPLO with Josephson-junction circuitry and operate it as a sensitive phase detector. Using a PPLO, we demonstrate the demodulation of a weak binary phase-shift keying microwave signal of the order of a femtowatt. We apply PPLO to dispersive readout of a superconducting qubit, and achieved high-fidelity, single-shot and non-destructive readout with Rabi-oscillation contrast exceeding 90%. Parametric phase-locked oscillators were first developed in the 1950s as a way of electrically storing and controlling information. Lin et al. now show that a modern version of this concept using superconducting circuits enables high-fidelity, single-shot and non-destructive measurement of a qubit.

Polycrystalline samples of Ca 2.7 Bi 0.3 Co 4-x Fe x O 9+δ ( x  = 0.00, 0.025, 0.05, 0.10 and 0.15) have been prepared by conventional solid-state synthesis and their thermoelectric and magnetic properties measured. The X-ray diffraction patterns revealed that all the samples are single phase. The electrical resistivity results indicated that all the samples obey the variable range hopping in the low temperature regime. The thermopower of all the samples was positive, indicating that the predominant carriers are holes over the entire temperature range. The electrical resistivity and thermopower were increased with increasing Fe content. Among the samples, Ca 2.95 Bi 0.10 Co 3.95 Fe 0.05 O 9+δ had the highest dimensionless figure of merit of 0.102 at 300 K. Magnetic measurements indicated that all the samples exhibit a low-spin state of cobalt ion. The effective magnetic moments were decreased with increasing Fe content.

Polycrystalline samples of [Ca.sub.3-x][Bi.sub.x][Co.sub.4][O.sub.9+δ] (x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.30) have been prepared by conventional solid-state synthesis. Thermopower of all the samples is positive, indicating that the predominant carriers are holes over the entire temperature range. The resistivity of all the samples, except the one with x = 0.30, exhibits nonmetal to metal transition ([T.sub.MI]) in the low temperature regime. The resistivity results indicate that all the doped samples obey the variable range hopping in the low temperature regime. The [T.sub.MI] and [T.sup.*] (transition temperature from Fermi liquid metal to incoherent metal) increase, and the slope of A value (Fermiliquid transport coefficient) decreases with the increasing Bi content due to an increase in chemical pressure in the lattice. Among the samples, [Ca.sub.2.7][Bi.sub.0.3][Co.sub.4][O.sub.9+δ] has the highest dimensionless figure of merit of 0.091 at 300 K. This value represents an improvement of about 135 % compared to the undoped [Ca.sub.3][Co.sub.4][O.sub.9+δ]. Magnetic measurements indicate that all the samples exhibit a low-spin state of cobalt ion. The ferrimagnetic transition temperature is suppressed by the Bi dopant. These results suggest that Bi is an effective doping element for improving the thermoelectric properties of [Ca.sub.3][Co.sub.4][O.sub.9+δ].

The effect of Fe ion doping on the low-temperature thermoelectric and magnetic properties of Ca 2.9 Bi 0.1 Co 4−x Fe x O 9+δ (x = 0.00, 0.025, 0.05 and 0.10) have been investigated. The samples were prepared by conventional solid-state synthesis. The X-ray diffraction patterns revealed that all the samples are single phase. The electrical resistivity results indicated that all the samples obey the variable range hopping in the low temperature regime. The T * (transition temperature from Fermi liquid metal to incoherent metal) was increased and the slope of A value (Fermi-liquid transport coefficient) was decreased with increasing Fe content. The thermopower of all the samples was positive, indicating that the predominant carriers are holes over the entire temperature range. The electrical resistivity, thermopower and total thermal conductivity were decreased with increasing Fe content. Among the doped samples, Ca 2.95 Bi 0.10 Co 3.90 Fe 0.10 O 9+δ had the highest dimensionless figure of merit of 0.056 at 300 K. Magnetic measurements indicated that all the samples exhibit a low-spin state of cobalt ion. The effective magnetic moments were decreased with increasing Fe content.

The search for the ferromagnetic quantum critical point (FM QCP) has always been a captivating research topic in the scientific community. In pursuit of this goal, we introduced nonmagnetic transition metals to alloy with elemental nickel, and studied the magnetic properties of nickel binary alloys Ni1-xMox and Ni1-yCuy as a function of x and y up to the critical concentrations x_{cr} and y_{cr} at which the FM transition T_C disappears. T_C-x(y) phase diagrams were constructed via the Arrott-Noakes scaling of magnetization data. An enhanced Sommerfeld coefficient (the value of C/T as T \\rightarrow 0) is observed near y_{cr}, manifesting the effect of quantum fluctuations near the quantum phase transition. It is evident that C/T diverges with -logT down to 0.1 K in the vicinity of y_{cr}, suggests the plausible FM QCP in Ni1-yCuy. However, in the case of Ni1-xMox, although the enhancement of the Sommerfeld coefficient is also observed near x_{cr}, the spin glass behavior is identified through the ac magnetic susceptibility measurement. This observation rules out the possibility of the existence of the FM QCP in Ni1-xMox.

We study microwave response of a Josephson parametric oscillator consisting of a superconducting transmission-line resonator with an embedded dc-SQUID. The dc-SQUID allows to control the magnitude of a Kerr nonlinearity over the ranges where it is smaller or larger than the photon loss rate. Spectroscopy measurements reveal the change of the microwave response from a classical Duffing oscillator to a Kerr parametric oscillator in a single device. In the single-photon Kerr regime, we observe parametric oscillations with a well-defined phase of either \\(0\\) or \\(\\pi\\), whose probability can be controlled by an externally injected signal.

The dopamine transporter (DAT) regulates extracellular dopamine DA levels and is an important site of action for amphetamine and cocaine. Amphetamine and cocaine increase extracellular levels of DA by acting on the DAT; thus, variations in DAT binding sites or activity might influence the action of some drugs of abuse. It was hypothesized that streptozotocin-induced diabetes decreases amphetamine self-administration and that this behavioral change is accompanied by changes in DAT function. Separate groups of male rats responded to receive either amphetamine (0.03 mg/kg/infusion), cocaine (0.25 mg/kg/infusion), or food before and for 7 days after receiving streptozotocin. Rats were sacrificed and [ 3 H]DA uptake and [ 3 H]WIN 35,428 binding were measured in the striatum. In a second study, rats could self-administer one of several different doses of amphetamine (0.01–0.178 mg/kg/infusion) before and after receiving streptozotocin. In streptozotocin-treated rats, a marked decrease in staining for insulin in pancreatic sections was paralleled by a more than doubling in blood glucose levels. Streptozotocin significantly decreased the number of amphetamine infusions without changing the number of cocaine infusions or food pellets received. Streptozotocin increased DA uptake (V max ) 1.6- or 2.4-fold in rats that responded for food or amphetamine and increased 3-fold the K m for DA only in rats that responded for food; however, [ 3 H]WIN 35,428 binding was not changed in any rat. In the second study, streptozotocin only decreased amphetamine self-administration thereby supporting the view that streptozotocin does not simply decrease the potency of amphetamine. These results demonstrate a selective decrease in amphetamine self-administration in diabetic rats that was associated with increased DAT function in the striatum. Collectively, these studies suggest that insulin pathways in the brain may play an important role in regulating DAT activity and amphetamine action.

We propose a two-qubit quantum logic gate between a superconducting atom and a propagating microwave photon. The atomic qubit is encoded on its lowest two levels and the photonic qubit is encoded on its carrier frequencies. The gate operation completes deterministically upon reflection of a photon, and various two-qubit gates (SWAP, \\(\\sqrt{\\rm SWAP}\\), and Identity) are realized through {\\it in situ} control of the drive field. The proposed gate is applicable to construction of a network of superconducting atoms, which enables gate operations between non-neighboring atoms.