Superconducting Transmission Line Resonator Research Articles

Coherent Control of Collective Spontaneous Emission through Self-Interference.

As one of the central topics in quantum optics, collective spontaneous emission such as superradiance has been realized in a variety of systems. This Letter proposes an innovative scheme to coherently control collective emission rates via a self-interference mechanism in a nonlinear waveguide setting. The self-interference is made possible by photon backward scattering incurred by quantum scatterers in a waveguide working as quantum switches. Whether the interference is constructive or destructive is found to depend strongly on the distance between the scatterers and the emitters. The interference between two propagation pathways of the same photon leads to controllable superradiance and subradiance, with their collective decay rates much enhanced or suppressed (also leading to hyperradiance or population trapping). Furthermore, the self-interference mechanism is manifested by an abrupt change in the emission rates in real time. An experimental setup based on superconducting transmission line resonators and transmon qubits is further proposed to realize controllable collective emission rates.

High kinetic inductance NbTiN superconducting transmission line resonators in the very thin film limit

We examine the DC and radio frequency (RF) response of superconducting transmission line resonators comprised of very thin NbTiN films, <12 nm in thickness, in the high-temperature limit, where the photon energy is less than the thermal energy. The resonant frequencies of these superconducting resonators show a significant nonlinear response as a function of RF input power, which can approach a frequency shift of Δf=−0.15% in a −20 dB span in the thinnest film. The strong nonlinear response allows these very thin film resonators to serve as high kinetic inductance parametric amplifiers.

Spectroscopic observation of the crossover from a classical Duffing oscillator to a Kerr parametric oscillator

We study microwave response of a Josephson parametric oscillator consisting of a superconducting transmission-line resonator with an embedded DC-superconducting quantum interference device (-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 in 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 $\ensuremath{\pi}$, whose probability can be controlled by an externally injected signal.

Coupling-modulation–mediated generation of stable entanglement of superconducting qubits via dissipation

We propose an experimentally feasible scheme for the dissipative generation of stable entanglement of superconducting qubits via coupling modulation without applying any drives on qubits and resonator. Firstly, we study the circuit of one superconducting transmission line resonator coupled to two separated qubits via two superconducting quantum interference devices (SUQIDs). By modulating the inductance of the SQUIDs via external fluxes, we can tailor an appropriate qubit-resonator coupling with both red- and blue-sideband interactions. Combined with the photon loss of the resonator, the two qubits can be autonomously steered into a long-lived entangled state with high fidelity. Moreover, we extend the model to one resonator coupled to two separated qubit chains, each of which contains N linearly coupled superconducting qubits. We show that the lossy resonator can drive the whole system into a unique dark state, i.e., a series of N entangled pairs of qubits across the chains can be stabilized at the stationary state. So, the present work enables the preparation of a stable long-range entangled state between the two qubits in the end sites of the chains, which plays an important role for implementing scalable quantum computation and quantum communication.

Topological Photonics on Superconducting Quantum Circuits with Parametric Couplings

AbstractTopological phases of matter are an exotic phenomenon in modern condensed matter physics, which has attracted much attention due to the unique boundary states and transport properties. Recently, this topological concept in electronic materials has been exploited in many other fields of physics. Motivated by designing and controlling the behavior of electromagnetic waves in optical, microwave, and sound frequencies, topological photonics emerges as a rapid growing research field. Due to the flexibility and diversity of superconducting quantum circuits system, it is a promising platform to realize exotic topological phases of matter and to probe and explore topologically‐protected effects in new ways. Here, theoretical and experimental advances of topological photonics on superconducting quantum circuits—via the experimentally demonstrated parametric tunable coupling techniques, including using of the superconducting transmission line resonator, superconducting qubits, and their coupled system—are reviewed. On superconducting circuits, the flexible interactions and intrinsic nonlinearity make topological photonics in this system not only a simple photonic analog of topological effects for novel devices, but also a realm of exotic but less‐explored fundamental physics.

All‐Resonance Controlled‐Phase Gate on Two Nonlocal Nitrogen‐Vacancy Center Ensembles Assisted by a Superconducting Quantum Circuit

AbstractThe realization of universal quantum logical gates on nonlocal nitrogen‐vacancy center ensembles (NVEs) is a basic task for universal quantum computing with NVEs. In contrast to previous works on the construction of gates, a one‐step all‐resonance scheme is proposed to construct a controlled‐phase gate on two nonlocal NVEs that are coupled to different superconducting transmission line resonators connected by a superconducting transmon qubit. The gate can be easily realized using only one step. Moreover, the all‐resonance operation allows the gate to be achieved within a short time. By considering the feasible parameters obtained in the experiments, this gate can be completed within 101 ns with a high fidelity of approximately 97.8%, which has reached the threshold of fault‐tolerance quantum computing.

Tunable Topological Beam Splitter in Superconducting Circuit Lattice

In the usual Su–Schrieffer–Heeger (SSH) model with an even number of lattice sites, the topological pumping between left and right edge states cannot be easily realized since the edge states occupy two-end sites simultaneously. Here we propose a scheme to investigate the topological edge pumping in an even-sized periodically modulated SSH model mapped by a one dimensional superconducting transmission line resonators array. We find that the photon initially prepared in the first resonator can be finally observed at the two-end resonators with a certain proportion. The final photon splitting at the two-end resonators indicates that the present superconducting circuit is expected to realize the topological beam splitter. Further, we demonstrate that the splitting proportion between the two-end resonators can be arbitrarily tuned from 1 to 0, implying the potential feasibility of implementing the tunable topological beam splitter. Meanwhile, we also show that the tunable topological beam splitter is immune to the mild disorder added into the system due to the topology protection of the zero energy modes, and find that the tunable topological beam splitter is much more robust to the global on-site disorder compared with the nearest neighbor disorder. Our work greatly extends the practical application of topological matter in quantum information processing and opens up a new way towards the engineering of topological quantum optical device.

Quantum simulation of clustered photosynthetic light harvesting in a superconducting quantum circuit

We propose a scheme to simulate the exciton energy transfer (EET) of photosynthetic complexes in a quantum superconducting circuit system. Our system is composed of two pairs of superconducting charge qubits coupled to two separated high-Q superconducting transmission line resonators (TLRs) connected by a capacitance. When the frequencies of the qubits are largely detuned with those of the TLRs, we simulate the process of the EET from the first qubit to the fourth qubit. By tuning the couplings between the qubits and the TLRs, and the coupling between the two TLRs, we can modify the effective coupling strengths between the qubits and thus demonstrate the geometric effects on the EET. It is shown that a moderate clustered geometry supports optimal EET by using exciton delocalization and energy matching condition. And the population loss during the EET has been trapped in the two TLRs.

Propagation of microwave photons along a synthetic dimension

The evenly spaced modes of an electromagnetic resonator are coupled to each other by appropriate time modulation, leading to dynamics analogous to those of particles hopping between different sites of a lattice. This substitution of a real spatial dimension of a lattice with a ``synthetic'' dimension in frequency space greatly reduces the hardware complexity of an analog quantum simulator. Complex control and readout of a highly multimoded structure can thus be accomplished with very few physical control lines. We demonstrate this concept with microwave photons in a superconducting transmission line resonator by modulating the system parameters at frequencies near the resonator's free spectral range and observing propagation of photon wave packets in time domain. The linear propagation dynamics are equivalent to a tight-binding model, which we probe by measuring scattering parameters between frequency sites. We extract an approximate tight-binding dispersion relation for the synthetic lattice and initialize photon wave packets with well-defined quasimomenta and group velocities. As an example application of this platform in simulating a physical system, we demonstrate Bloch oscillations associated with a particle in a periodic potential and subject to a constant external field. The simulated field strongly affects the photon dynamics despite photons having zero charge. Our observation of photon dynamics along a synthetic frequency dimension generalizes immediately to topological photonics and single-photon power levels, and expands the range of physical systems addressable by quantum simulation.

Measurement of Spin Singlet-Triplet Qubit in Quantum Dots Using Superconducting Resonator**Supported by the National Basic Research Programme of China (No. 2017YFA0304100), and the National Natural Science Foundation of China (No. 11974336).

The spin qubit in quantum dots is one of the leading platforms for quantum computation. A crucial requirement for scalable quantum information processing is the high efficient measurement. Here we analyze the measurement process of a quantum-dot spin qubit coupled to a superconducting transmission line resonator. Especially, the phase shift of the resonator is sensitive to the spin states and the gate operations. The response of the resonator can be used to measure the spin qubit efficiently, which can be extend to read out the multiple spin qubits in a scalable solid-state quantum processor.

Dissipative generation of steady-state squeezing of superconducting resonators via parametric driving

A dissipative method is proposed for generating the squeezed state of a microwave field in a superconducting transmission line resonator, which is coupled to a superconducting qubit. When the resonator is subject to the parametric driving, the qubit-resonator coupling can be exponentially enhanced. We show that the dissipation of the qubit as a resource can be used to produce and stabilize the single-mode squeezed state of the superconducting resonator at steady state. Compared with previous works, our scheme has the advantage that only a single drive is used for the quantum state preparation, which can simplify the experimental operations. Combined with the quantum interference effect, we also generalize our idea to the dissipative preparation of a two-mode squeezed state in two directly coupled superconducting resonators. The present work may have many potential applications in the field of quantum information processing with superconducting circuits.

Practical one-step synthesis of multipartite entangled states on superconducting circuits

Quantum entanglement is an important resource for quantum information processing tasks. However, realistic multipartite entangled state production is very difficult. In this paper, we propose an efficient single-step scheme for generating many body Greenberger–Horne–Zeilinger (GHZ) states on superconducting circuits by using a superconducting transmission-line resonator (TLR) interact with [Formula: see text] superconducting transmon qubits. The distinct merit of our proposal is that it does not require the qubit-resonator coupling strengths to be the same, which is usually impractical experimentally, and thus is one of the main reasons for entanglement generation infidelity in previous single-step schemes. The removing of the uniform interaction requirement is achieved by modulating the qubits splitting frequencies with ac microwave fields, which results in tunable individual qubit-resonator coupling strength, and thus effective uniform qubit–qubit interaction Hamiltonian can be obtained. Since microwave control is conventional nowadays, our proposal can be directly tested experimentally, which makes previous multipartite entangled states generation schemes more efficient.

Stabilizing Bell states of two separated superconducting qubits via quantum reservoir engineering

We propose a quantum reservoir engineering approach for stabilizing Bell states of two superconducting qubits. The system under consideration consists of two linearly coupled superconducting transmission line resonators and two separated flux qubits, one of which is interacted with one resonator. Applying external driving fields to tailor appropriate qubit-resonator interactions, we show that dissipative photons of the resonators can be exploited to autonomously drive and stabilize the two flux qubits into an approximate Bell state at the stationary state. Because of using the dissipative dynamical process, the present approach does not need to well prepare the initial state of the system and exactly monitor the evolution time. Compared with previous schemes, the present one has the remarkable features that the generation of the entangled state is implemented at a single-photon quantum level, and all four Bell states can be generated and stabilized on demand by changing the external driving parameters. Our result may have useful applications for the realization of quantum computation with superconducting quantum circuits.

Two-mode squeezed states of two separated nitrogen-vacancy-center ensembles coupled via dissipative photons of superconducting resonators

We propose an efficient method for generating two-mode squeezed states of the collective excitation of two nitrogen-vacancy-center ensembles (NVEs), which are magnetically coupled to two interacting superconducting transmission line resonators via photon hopping, respectively. By applying the external driving fields to induce Raman transitions between the ground-state sublevels of the nitrogen-vacancy center, an effective interaction between the spin ensembles and the resonators can be engineered. We show that the dissipative quantum dynamical process of the two resonators can be employed to steer the two NVEs into a two-mode squeezed state. By comparison with previous proposals, our scheme does not need either an extra superconducting qubit, or external squeezing resource. The present work may have potential applications for implementing NVE-based hybrid quantum computation.

Quadrature squeezing of the mechanical mode in a superconducting electromechanical system

We propose a scheme for realizing quadrature squeezing of the mechanical mode in a superconducting electromechanical system, where a nanomechanical resonator (NAMR) is coupled to a superconducting transmission line resonator (STLR) via a superconducting quantum interference device (SQUID), and the SQUID acts as a qubit. Under a large detuning condition, we use the Fröhlich-Nakajima transformation to adiabatically eliminate the qubit and obtain an effective Hamiltonian for the STLR and the NAMR. Our results show that a strong squeezing effect (beyond 3 dB limit) can occur in the NAMR, and the squeezing degree can be optimized by controlling the strength of the driving field and the dissipation ratio of the system. One of the most notable features of our results is the universality, i.e. the results only depend on a few scaled quantities, not on too many parameters.

Photon blockade with cross-Kerr nonlinearity in superconducting circuits

We theoretically investigate the photon statistical properties of a weakly-driven circuit quantum electrodynamic system with a cross-Kerr nonlinearity, which is built from two coupled transmon qubits through a superconducting quantum interference device (SQUID). We show that when two resonators are resonant with each other, photon blockade and sub-Poissonian photon statistics in the first superconducting transmission line resonator (TLR), TLR1, can be achieved by modulating the resonator-driving detunings and the cross-Kerr nonlinearity. Moreover, the optimal conditions for obtaining sub-Poissonian statistics are put forward through analytical derivations, which are in good agreement with those obtained by numerical simulations. We also examine the role of the resonator–resonator hopping interaction for photon statistics in TLR1 by numerically analyzing the case where the frequencies of two resonators are far detuned from each other. Due to the cutoff of the indirect transition paths in this case, the output field always acquires super-Poissonian statistics. In addition, a physical model with a SQUID embedded in TLR1 is proposed to tune the detuning between two TLRs, making it possible to demonstrate the importance of the resonator–resonator hopping interaction in obtaining a single-photon blockade. Thereby, our model of two coupled resonators with cross-Kerr nonlinearity has the potential to engineer the photon statistics through operating on the system parameters.

Quantum heat engine with coupled superconducting resonators.

We propose a quantum heat engine composed of two superconducting transmission line resonators interacting with each other via an optomechanical-like coupling. One resonator is periodically excited by a thermal pump. The incoherently driven resonator induces coherent oscillations in the other one due to the coupling. A limit cycle, indicating finite power output, emerges in the thermodynamical phase space. The system implements an all-electrical analog of a photonic piston. Instead of mechanical motion, the power output is obtained as a coherent electrical charging in our case. We explore the differences between the quantum and classical descriptions of our system by solving the quantum master equation and classical Langevin equations. Specifically, we calculate the mean number of excitations, second-order coherence, as well as the entropy, temperature, power, and mean energy to reveal the signatures of quantum behavior in the statistical and thermodynamic properties of the system. We find evidence of a quantum enhancement in the power output of the engine at low temperatures.

Polarization entanglement purification of nonlocal microwave photons based on the cross-Kerr effect in circuit QED

Microwave photons have become very important qubits in quantum communication as the first quantum satellite has been launched successfully. Therefore, it is a necessary and meaningful task for ensuring the high security and efficiency of microwave-based quantum communication in practice. Here, we present an original polarization entanglement purification protocol for nonlocal microwave photons based on the cross-Kerr effect in circuit quantum electrodynamics (QED). Our protocol can solve the problem that the purity of maximally entangled states used for constructing quantum channels will decrease due to decoherence from environment noise. This task is accomplished by means of the polarization parity-check quantum nondemolition (QND) detector, the bit-flipping operation, and the linear microwave elements. The QND detector is composed of several cross-Kerr effect systems which can be realized by coupling two superconducting transmission line resonators to a superconducting molecule with the N-type level structure. We give the applicable experimental parameters of QND measurement system in circuit QED and analyze the fidelities. Our protocol has good applications in long-distance quantum communication assisted by microwave photons in the future, such as satellite quantum communication.

Transmission-line resonators for the study of individual two-level tunneling systems

Parasitic two-level tunneling systems (TLS) emerge in amorphous dielectrics and constitute a serious nuisance for various microfabricated devices, where they act as a source of noise and decoherence. Here, we demonstrate a new test bed for the study of TLS in various materials which provides access to properties of individual TLS as well as their ensemble response. We terminate a superconducting transmission-line resonator with a capacitor that hosts TLS in its dielectric. By tuning TLS via applied mechanical strain, we observe the signatures of individual TLS strongly coupled to the resonator in its transmission characteristics and extract the coupling components of their dipole moments and energy relaxation rates. The strong and well-defined coupling to the TLS bath results in pronounced resonator frequency fluctuations and excess phase noise, through which we can study TLS ensemble effects such as spectral diffusion, and probe theoretical models of TLS interactions.

Entanglement concentration of microwave photons based on the Kerr effect in circuit QED

In recent years, superconducting qubits show great potential in quantum computation. Hence, microwave photons become very interesting qubits for quantum information processing assisted by superconducting quantum computation. Here, we present the first protocol for the entanglement concentration on microwave photons, resorting to the cross-Kerr effect in circuit quantum electrodynamics (QED). Two superconducting transmission line resonators (TLRs) coupled to superconducting molecule with the N-type level structure induce the effective cross-Kerr effect for realizing the quantum nondemolition (QND) measurement on microwave photons. With this device, we present a two-qubit polarization parity QND detector on the photon states of the superconducting TLRs, which can be used to concentrate efficiently the nonlocal non-maximally entangled states of microwave photons assisted by several linear microwave elements. This protocol has a high efficiency and it may be useful for solid-state quantum information processing assisted by microwave photons.