I am going to post here all newly submitted articles on the arXiv related to superconducting circuits. If your article has been accidentally forgotten, feel free to contact me
08
Aug
2018
Quantum generative adversarial learning in a superconducting quantum circuit
Generative adversarial learning is one of the most exciting recent breakthroughs in machine learning—a subfield of artificial intelligence that is currently driving a revolution
in many aspects of modern society. It has shown splendid performance in a variety of challenging tasks such as image and video generations. More recently, a quantum version of generative adversarial learning has been theoretically proposed and shown to possess the potential of exhibiting an exponential advantage over its classical counterpart. Here, we report the first proof-of-principle experimental demonstration of quantum generative adversarial learning in a superconducting quantum circuit. We demonstrate that, after several rounds of adversarial learning, a quantum state generator can be trained to replicate the statistics of the quantum data output from a digital qubit channel simulator, with a high fidelity (98.8% on average) that the discriminator cannot distinguish between the true and the generated data. Our results pave the way for experimentally exploring the intriguing long-sought-after quantum advantages in machine learning tasks with noisy intermediate-scale quantum devices.
Nonadiabatic geometric quantum computation with parametrically tunable coupling
The implementation of nonadiabatic geometric quantum computation is promising since its robustness against certain types of noises. Meanwhile, it is also challenging due to the need
of complex control on the quantum multiple and/or multi-level systems. Here, we propose to implement nonadiabatic geometric quantum computation on a two-dimensional square superconducting qubit lattice. In our construction of the geometric quantum gates, we merely adopt simple and experimentally accessible control over the quantum systems, which only involve their qubit states. Specifically, our scheme is achieved by parametrically tunable all-resonant interactions, which leads to high-fidelity quantum gates. Moreover, this simple implementation can be conveniently generalized to a composite scenario, which can further suppress the systematic error during the gate operations. In addition, universal nonadiabatic geometric quantum gates in decoherence-free subspaces can also be implemented based on the tunable coupling between only two transmon qubits, without consulting to multiple qubits and only using two physical qubits to construct the logical qubit. Therefore, our scheme possesses promising prospects for experimental implementation of geometric quantum computation.
Hybrid Two-Qubit Gate using Circuit QED System with Triple-Leg Stripline Resonator
We theoretically propose a circuit QED system implemented with triple-leg stripline resonator (TSR). Unlikely from linear stripline resonator, the fundamental intra-cavity microwave
modes of the TSR are two-fold degenerate. When a superconducting qubit is placed near one of the TSR legs, one fundamental mode is directly coupled to the qubit, while the other one remains uncoupled. Our system closely resembles an optical cavity QED system, where an atom in a cavity couples only to the incident photon with a specific polarization by placing a polarization beamsplitter in front of the optical cavity.
Using our circuit QED system, we have theoretically studied a two-qubit quantum gate operation in a hybrid qubit composed of flying microwave qubit and superconducting qubit. We have demonstrated that for the hybrid qubit, the quantum controlled phase flip (CPF) gate can be reliably implemented for the experimentally available set of parameters.
07
Aug
2018
eQASM: An Executable Quantum Instruction Set Architecture
Bridging the gap between quantum software and hardware, recent research proposed a quantum control microarchitecture QuMA which implements the quantum microinstruction set QuMIS. However,
QuMIS does not offer feedback control, and is tightly bound to the hardware implementation. Also, as the number of qubits grows, QuMA cannot fetch and execute instructions fast enough to apply all operations on qubits on time. Known as the quantum operation issue rate problem, this limitation is aggravated by the low information density of QuMIS instructions.
In this paper, we propose an executable quantum instruction set architecture (QISA), called eQASM, that can be translated from the quantum assembly language (QASM), supports feedback, and is executed on a quantum control microarchitecture. eQASM alleviates the quantum operation issue rate problem by efficient timing specification, single-operation-multiple-qubit execution, and a very-long-instruction-word architecture. The definition of eQASM focuses on the assembly level to be expressive. Quantum operations are configured at compile time instead of being defined at QISA design time. We instantiate eQASM into a 32-bit instruction set targeting a seven-qubit superconducting quantum processor. We validate our design by performing several experiments on a two-qubit quantum processor.
03
Aug
2018
Observation of Multiphoton Frequency Conversion in Superconducting Circuits
Multiphoton up/down conversion in a transmon circuit, driven by a pair of microwaves tuned near and far off the qubit resonance, has been observed. The experimental realization of these
high order non-linear processes is accomplished in the three-photon regime, when the transmon is coupled to weak bichromatic microwave fields with the same Rabi frequencies. A many-mode Floquet formalism, with longitudinal coupling, is used to simulate the quantum interferences in the absorption spectrum that manifest the multiphoton pumping processes in the transmon qubit. An intuitive graph theoretic approach is used to introduce to provide effective Hamiltonians that elucidate main features of the Floquet results. The analytical solutions also illustrate how controllability is achievable for desired single- or multiphoton pumping processes in a wide frequency range.
02
Aug
2018
Tunable superconducting two-chip lumped element resonator
We have fabricated and investigated a stacked two-chip device, consisting of a lumped element resonator on one chip, which is side-coupled to a coplanar waveguide transmission line
on a second chip. We present a full model to predict the behavior of the device dependent on the position of the lumped element resonator with respect to the transmission line. We identify different regimes, in which the device can be operated. One of them can be used to tune the coupling between the two subsystems. Another regime enables frequency tunability of the device, without leaving the over-coupled limit for internal quality factors of about 10^4, while in the last regime the resonator properties are insensitive against small variations of the position. Finally, we have measured the transmission characteristics of the resonator for different positions, demonstrating a good agreement with the model.
01
Aug
2018
Nonadiabatic holonomic quantum computation on coupled transmons with ancillary
The physical implementation of holonomic quantum computation is challenging due to the needed complex controllable interactions on multilevel quantum systems. Here we propose to implement
the nonadiabatic holonomic quantum computation with the conventional capacitive coupled superconducting transmon qubits, where a universal set of quantum gates is constructed with the help of the interaction to an auxiliary qubit rather than consulting to delicate control over an auxiliary level of multilevel quantum systems. Explicitly, these quantum gates are realized by tunable interactions in an all-resonant way, which leads to high-fidelity gate operations. In this way, the distinct merit of our scheme is that we only use the two lowest levels of a transmon to form the qubit states. In addition, the auxiliary qubits are in their ground states before and after every gate operation. Therefore, our scheme paves a promising way towards the practical realization of high-fidelity nonadiabatic holonomic quantum computation.
25
Jul
2018
Adiabatic Superconducting Artificial Neural Network: Basic Cells
We consider adiabatic superconducting cells operating as an artificial neuron and synapse of a multilayer perceptron (MLP). Their compact circuits contain just one and two Josephson
junctions, respectively. While the signal is represented as magnetic flux, the proposed cells are inherently nonlinear and close-to-linear magnetic flux transformers. The neuron is capable of providing a one-shot calculation of sigmoid and hyperbolic tangent activation functions most commonly used in MLP. The synapse features by both positive and negative signal transfer coefficients in the range ~ (-0.5,0.5). We briefly discuss implementation issues and further steps toward multilayer adiabatic superconducting artificial neural network which promises to be a compact and the most energy-efficient implementation of MLP.
Resonance inversion in a superconducting cavity coupled to artificial atoms and a microwave background
We demonstrate how heating of an environment can invert the line shape of a driven cavity. We consider a superconducting coplanar cavity coupled to multiple artificial atoms. The measured
cavity transmission is characterized by Fano-type resonances with a shape that is continuously tunable by bias current through nearby (magnetic flux) control lines. In particular, the same dispersive shift of the microwave cavity can be observed as a peak or a dip. We find that this Fano-peak inversion is possible due to a tunable interference between a microwave transmission through a background, with reactive and dissipative properties, and through the cavity, affected by bias-current induced heating. The background transmission occurs due to crosstalk with the multiple control lines. We show how such background can be accounted for by a Jaynes- or Tavis-Cummings model with modified boundary conditions between the cavity and transmission-line microwave fields. A dip emerges when cavity transmission is comparable with background transmission and dissipation. We find generally that resonance positions determine system energy levels, whereas resonance shapes give information on system fluctuations and dissipation.
24
Jul
2018
Stabilized Cat in Driven Nonlinear Cavity: A Fault-Tolerant Error Syndrome Detector
low-weight operations with an ancilla to extract information about errors without causing backaction on the encoded system. Essentially, ancilla errors must not propagate to the encoded
system and induce errors beyond those which can be corrected. The current schemes for achieving this fault-tolerance to ancilla errors come at the cost of increased overhead requirements. An efficient way to extract error syndromes in a fault-tolerant manner is by using a single ancilla with strongly biased noise channel. Typically, however, required elementary operations can become challenging when the noise is extremely biased. We propose to overcome this shortcoming by using a bosonic-cat ancilla in a parametrically driven nonlinear cavity. Such a cat-qubit experiences only bit-flip noise and is stabilized against phase-flips. To highlight the flexibility of this approach, we illustrate the syndrome extraction process in a variety of codes such as qubit-based toric codes, bosonic cat- and Gottesman-Kitaev-Preskill (GKP) codes. Our results open a path for realizing hardware-efficient, fault-tolerant error syndrome extraction.