32 research outputs found
Construction of controlled-NOT gate based on microwave-activated phase (MAP) gate in two transmon system
We experimentally constructed an all-microwave scheme for the controlled-NOT
(cNOT) gate between two superconducting transmon qubits in a three dimensional
cavity. Our cNOT gate is based on the microwave-activated phase (MAP) gate,
which requires an additional procedure to compensate the accumulated phases
during the operation of the MAP gate. We applied Z-axis phase gates using
microwave hyperbolic secant pulse on both qubits with adequate rotation angles
systematically calibrated by separate measurements.We evaluated the gate
performance of the constructed cNOT gate by performing two-qubit quantum
process tomography (QPT). Finally, we present the experimental implementation
of Deutsch-Jozsa algorithm using the cNOT gate
Observation of Kondo condensation in a degenerately doped silicon metal
When a magnetic moment is embedded in a metal, it captures itinerant
electrons to form the Kondo cloud1,2, which can spread out over a few
micrometres3,4. For a metal with dense magnetic impurities such that Kondo
clouds overlap with each other, correlated ground states are formed. When the
impurities form a regular lattice, the result is a heavy fermion or
anti-ferromagnetic order depending on the dominant interaction5,6. Even in the
case of random impurities, overlapping Kondo clouds are expected to form a
coherent ground state. Here, we examine this issue by performing electrical
transport and high-precision tunnelling density-of-states (DOS) spectroscopy
measurements in a highly P-doped crystalline silicon metal where
disorder-induced localized magnetic moments exist7. We detect the Kondo effect
in the resistivity of the Si metal below 2 K and an exotic pseudogap in the DOS
with gap edge peaks at a Fermi energy below 100 mK. The DOS gap and peaks are
tuned by applying an external magnetic field and transformed into a metallic
Altshuler-Aronov gap8 in the paramagnetic disordered Fermi liquid (DFL) phase.
We interpret this phenomenon as the Kondo condensation, the formation of a
correlated ground state of overlapping Kondo clouds, and its transition to a
DFL. The boundary between the Kondo condensation and DFL phases is identified
by analysing distinct DOS spectra in the magnetic field-temperature plane. A
detailed theoretical analysis using a holographic method 9 , 10 , 11 reproduces
the unusual DOS spectra, 1, supporting our scenario. Our work demonstrates the
observation of the magnetic version of Bardeen-Cooper-Shrieffer (BCS) pair
condensation and will be useful for understanding complex Kondo systems.Comment: 34 pages,5+6 figures, accepted in nature physic
Observation of Kondo condensation in a degenerately doped silicon metal
When a magnetic moment is embedded in a metal, it captures nearby itinerant electrons to form a so-called Kondo cloud. When magnetic impurities are sufficiently dense that their individual clouds overlap with each other they are expected to form a correlated electronic ground state. This is known as Kondo condensation and can be considered a magnetic version of Bardeen–Cooper–Schrieffer pair formation. Here, we examine this phenomenon by performing electrical transport and high-precision tunnelling density-of-states spectroscopy measurements in a highly P-doped crystalline silicon metal in which disorder-induced localized magnetic moments exist. We detect the Kondo effect in the resistivity of the Si metal at temperatures below 2 K and an unusual pseudogap in the density of states with gap edge peaks below 100 mK. The pseudogap and peaks are tuned by applying an external magnetic field and transformed into a metallic Altshuler–Aronov gap associated with a paramagnetic disordered Fermi liquid phase. We interpret these observations as evidence of Kondo condensation followed by a transition to a disordered Fermi liquid
Review of low-noise radio-frequency amplifiers based on superconducting quantum interference device
Superconducting quantum interference device (SQUID) is a sensitive detector of magnetic flux signals. Up to now, the main application of SQUIDs has been measurements of magnetic flux signals in the frequency range from near DC to several MHz. Recently, cryogenic low-noise radio-frequency (RF) amplifiers based on DC SQUID are under development aiming to detect RF signals with sensitivity approaching quantum limit. In this paper, we review the recent progress of cryogenic low-noise RF amplifiers based on SQUID technology. © 2014 Korea Institute of Applied Superconductivity and Cryogenics. All rights reserved11Nscopuskc
Quantum readout error mitigation via deep learning
Quantum computing devices are inevitably subject to errors. To leverage
quantum technologies for computational benefits in practical applications,
quantum algorithms and protocols must be implemented reliably under noise and
imperfections. Since noise and imperfections limit the size of quantum circuits
that can be realized on a quantum device, developing quantum error mitigation
techniques that do not require extra qubits and gates is of critical
importance. In this work, we present a deep learning-based protocol for
reducing readout errors on quantum hardware. Our technique is based on training
an artificial neural network with the measurement results obtained from
experiments with simple quantum circuits consisting of singe-qubit gates only.
With the neural network and deep learning, non-linear noise can be corrected,
which is not possible with the existing linear inversion methods. The advantage
of our method against the existing methods is demonstrated through quantum
readout error mitigation experiments performed on IBM five-qubit quantum
devices.Comment: 10 pages, 10 figure
Development of superconducting nanowire single photon detector (SNSPD) for communication wavelength of 1550 nm
We report our progress in the development of superconducting nanowire single photon detectors (SNSPDs). Single photon detector is the key component in quantum communication and quantum optics. Among various single photon detectors, SNSPDs show superior performance in detection efficiency, timing jitter, dark count, and count rate. We fabricate our devices with ultrathin niobium nitride (NbN) or amorphous molybdenum silicide (??-MoxSi1-x) films. 100 nm wide nanowire meander patterns are made on top of a distributed Bragg reflector (DBR). The detector is fiber-coupled and is operated below 2.5 K down to 0.8 K in a closed-cycle GM refrigerator. We use self-alignment scheme for the fiber-coupling in order to avoid possible drift due to the thermal contraction at low temperature. We present our measurement result of detection efficiency, dark count rate and reset time. We then discuss our further direction to increase the detector performance
Construction of controlled-NOT gate based on microwave-activated phase (MAP) gate in two transmon system
Abstract We experimentally constructed an all-microwave scheme for the controlled-NOT (cNOT) gate between two superconducting transmon qubits in a three dimensional cavity. Our cNOT gate is based on the microwave-activated phase (MAP) gate, which requires an additional procedure to compensate the accumulated phases during the operation of the MAP gate. We applied Z-axis phase gates using microwave hyperbolic secant pulse on both qubits with adequate rotation angles systematically calibrated by separate measurements. We evaluated the gate performance of the constructed cNOT gate by performing two-qubit quantum process tomography (QPT). Finally, we present the experimental implementation of the Deutsch-Jozsa algorithm using the cNOT gate
Flux-Driven Josephson Parametric Amplifier Fabricated Using the Nb/AlOx/Nb Trilayer Process
In this paper, we report a flux-driven Josephson parametric amplifier (JPA) fabricated using the Nb/AlOx/Nb Josephson junction process. The JPA consists of a parallel-plate type coupling capacitor and quarter-wavelength resonator terminated with a DC-SQUID. We adopt a simple process using well-established Nb trilayer technology. The overall configuration time of the Nb-based JPA can be shortened by measuring resonant frequency and its bias dependence in liquid helium. Amplification of the pre-tested device was demonstrated, showing a gain of 20 dB in a -3 dB bandwidth of 17 MHz in a 10 mK dilution fridge