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
03
Mai
2022
SWAP gate between a Majorana qubit and a parity-protected superconducting qubit
High fidelity quantum information processing requires a combination of fast gates and long-lived quantum memories. In this work, we propose a hybrid architecture, where a parity-protected
superconducting qubit is directly coupled to a Majorana qubit, which plays the role of a quantum memory. The superconducting qubit is based upon a π-periodic Josephson junction realized with gate-tunable semiconducting wires, where the tunneling of individual Cooper pairs is suppressed. One of the wires additionally contains four Majorana zero modes that define a qubit. We demonstrate that this enables the implementation of a SWAP gate, allowing for the transduction of quantum information between the topological and conventional qubit. This architecture combines fast gates, which can be realized with the superconducting qubit, with a topologically protected Majorana memory.
27
Apr
2022
High-fidelity quantum transduction with long coherence time superconducting resonators
We propose a novel quantum transduction hybrid system based on the coupling of long-coherence time superconducting cavities with electro-optic resonators to achieve high-efficiency
and high-fidelity in quantum communication protocols and quantum sensing.
21
Apr
2022
Superconducting microwave resonators with non-centrosymmetric nonlinearity
We investigated both theoretically and experimentally open-ended coplanar waveguide resonators with rf SQUIDs embedded in the central conductor at different positions. These rf SQUIDs
can be tuned by an external magnetic field and thus may exhibit the non-centrosymmetric nonlinearity of χ(2) type with suppressed Kerr nonlinearity. We demonstrated that this nonlinearity allows for efficient mixing of λ/2 and λ modes in the cavity and thus enables various parametric effects with three wave mixing. These effects are the second harmonic generation, the half tone generation, the parametric amplification in both degenerate and non-degenerate regimes and deamplification in degenerate regime.
19
Apr
2022
One hundred second bit-flip time in a two-photon dissipative oscillator
Current implementations of quantum bits (qubits) continue to undergo too many errors to be scaled into useful quantum machines. An emerging strategy is to encode quantum information
in the two meta-stable pointer states of an oscillator exchanging pairs of photons with its environment, a mechanism shown to provide stability without inducing decoherence. Adding photons in these states increases their separation, and macroscopic bit-flip times are expected even for a handful of photons, a range suitable to implement a qubit. However, previous experimental realizations have saturated in the millisecond range. In this work, we aim for the maximum bit-flip time we could achieve in a two-photon dissipative oscillator. To this end, we design a Josephson circuit in a regime that circumvents all suspected dynamical instabilities, and employ a minimally invasive fluorescence detection tool, at the cost of a two-photon exchange rate dominated by single-photon loss. We attain bit-flip times of the order of 100 seconds for states pinned by two-photon dissipation and containing about 40 photons. This experiment lays a solid foundation from which the two-photon exchange rate can be gradually increased, thus gaining access to the preparation and measurement of quantum superposition states, and pursuing the route towards a logical qubit with built-in bit-flip protection.
Quantum bath engineering of a high impedance microwave mode through quasiparticle tunneling
We demonstrate a new approach to dissipation engineering in microwave quantum optics. For a single mode, dissipation usually corresponds to quantum jumps, where photons are lost one
by one. Here, we are able to tune the minimal number of lost photons per jump to be two (or more) with a simple dc voltage. As a consequence, different quantum states experience different dissipation. Causality implies that the states must also experience different energy shifts. Our measurements of these Lamb shifts are in good agreement with the predictions of the Kramers-Kronig relations for single quantum states in a regime of highly non-linear bath coupling. This work opens new possibilities for quantum state manipulation in circuit QED, without relying on the Josephson effect.
18
Apr
2022
Entanglement properties of superconducting qubits coupled to a semi-infinite transmission line
Quantum entanglement, a key resource in quantum information processing, is reduced by interaction between the quantum system concerned and its unavoidable noisy environment. Therefore
it is of particular importance to study the dynamical properties of entanglement in open quantum systems. In this work, we mainly focus on two qubits coupled to an adjustable environment, namely a semi-infinite transmission line. The two qubits‘ relaxations, through individual channels or collective channel or both, can be adjusted by the qubits‘ transition frequencies. We examine entanglement dynamics in this model system with initial Werner state, and show that the phenomena of entanglement sudden death and revival can be observed. Due to the hardness of preparing the Werner state experimentally, we introduce a new type of entangled state called pseudo-Werner state, which preserves as much entangling property as the Werner state, and more importantly, is experiment friendly. Furthermore, we provide detailed procedures for generating pseudo-Werner state and studying entanglement dynamics with it, which can be straightforwardly implemented in a superconducting waveguide quantum electrodynamics system.
17
Apr
2022
Extensible circuit-QED architecture via amplitude- and frequency-variable microwaves
We introduce a circuit-QED architecture combining fixed-frequency qubits and microwave-driven couplers. In the appropriate frame, the drive parameters appear as tunable knobs enabling
selective two-qubit coupling and coherent-error suppression. We moreover introduce a set of controlled-phase gates based on drive-amplitude and drive-frequency modulation. We develop a theoretical framework based on Floquet theory to model microwave-activated interactions with time-dependent drive parameters, which we also use for pulse shaping. We perform numerical simulations of the gate fidelity for realistic circuit parameters, and discuss the impact of drive-induced decoherence. We estimate average gate fidelities beyond 99.9% for all-microwave controlled-phase operations with gate times in the range 50−120ns. These two-qubit gates can operate over a large drive-frequency bandwidth and in a broad range of circuit parameters, thereby improving extensibility. We address the frequency allocation problem for this architecture using perturbation theory, demonstrating that qubit, coupler and drive frequencies can be chosen such that undesired static and driven interactions remain bounded in a multi-qubit device. Our numerical methods are useful for describing the time-evolution of driven systems in the adiabatic limit, and are applicable to a wide variety of circuit-QED setups.
15
Apr
2022
Distinguishing parity-switching mechanisms in a superconducting qubit
Single-charge tunneling is a decoherence mechanism affecting superconducting qubits, yet the origin of excess quasiparticle excitations (QPs) responsible for this tunneling in superconducting
devices is not fully understood. We measure the flux dependence of charge-parity (or simply, „parity“) switching in an offset-charge-sensitive transmon qubit to identify the contributions of photon-assisted parity switching and QP generation to the overall parity-switching rate. The parity-switching rate exhibits a qubit-state-dependent peak in the flux dependence, indicating a cold distribution of excess QPs which are predominantly trapped in the low-gap film of the device. Moreover, we find that the photon-assisted process contributes significantly to both parity switching and the generation of excess QPs by fitting to a model that self-consistently incorporates photon-assisted parity switching as well as inter-film QP dynamics.
14
Apr
2022
Simple coplanar waveguide resonator mask targeting metal-substrate interface
This white paper presents a single-layer mask, found at this https URL. It is designed for fabrication of superconducting microwave resonators towards 1:1 comparisons of dielectric
losses from the metal-substrate interface. Finite-element electromagnetic simulations are used to determine participation ratios of the four major regions of the on-chip devices, as well as to confirm lack of crosstalk between neighboring devices and demonstrate coupling tunability over three orders of magnitude. This mask is intended as an open-source community resource for facilitating precise and accurate comparisons of materials in the single-photon, millikelvin regime.
08
Apr
2022
Efficient scheme for realizing a multiplex-controlled phase gate with photonic qubits in circuit quantum electrodynamics
We propose an efficient scheme to implement a multiplex-controlled phase gate with multiple photonic qubits simultaneously controlling one target photonic qubit based on circuit quantum
electrodynamics (QED). For convenience, we denote this multiqubit gate as MCP gate. The gate is realized by using a two-level coupler to couple multiple cavities. The coupler here is a superconducting qubit. This scheme is simple because the gate implementation requires only \textit{one step} of operation. In addition, this scheme is quite general because the two logic states of each photonic qubit can be encoded with a vacuum state and an arbitrary non-vacuum state (e.g., a Fock state, a superposition of Fock states, a cat state, or a coherent state, etc.) which is orthogonal or quasi-orthogonal to the vacuum state. The scheme has some additional advantages: Because only two levels of the coupler are used, i.e., no auxiliary levels are utilized, decoherence from higher energy levels of the coupler is avoided; the gate operation time does not depend on the number of qubits; and the gate is implemented deterministically because no measurement is applied. As an example, we numerically analyze the circuit-QED based experimental feasibility of implementing a three-qubit MCP gate with photonic qubits each encoded via a vacuum state and a cat state. The scheme can be applied to accomplish the same task in a wide range of physical system, which consists of multiple microwave or optical cavities coupled to a two-level coupler such as a natural or artificial atom.