We report parametric amplification of a microwave signal in a Kerr medium formed from superconducting qubits. Two mutually coupled flux qubits, embedded in the current antinode of a superconducting coplanar waveguide resonator, are used as a nonlinear element. Shared Josephson junctions provide the qubit-resonator coupling, resulting in a device with a tunable Kerr constant (up to 3 × 10−3) and a measured gain of about 20 dB. This arrangement represents a unit cell which can be straightforwardly extended to a quasi one-dimensional quantum metamaterial with large tunable Kerr nonlinearity, providing a basis for implementation of wide-band travelling wave parametric amplifiers.
We report parametric amplification of a microwave signal in a Kerr medium formed from superconducting qubits. Two mutually coupled flux qubits, embedded in the current antinode of a superconducting coplanar waveguide resonator, are used as a nonlinear element. Shared Josephson junctions provide the qubit-resonator coupling, resulting in a device with a tunable Kerr constant (up to 3 × 10−3) and a measured gain of about 20 dB. This arrangement represents a unit cell which can be straightforwardly extended to a quasi one-dimensional quantum metamaterial with large tunable Kerr nonlinearity, providing a basis for implementation of wide-band travelling wave parametric amplifiers.
We develop a novel concept of a Josephson traveling-wave parametric amplifier with three-wave mixing. The proposed amplifier consists of a microwave transmission line formed by a serial array of nonhysteretic one-junction SQUIDs. These SQUIDs are flux-biased such that the phase drops across the Josephson junctions are equal to 90°. This one-dimensional metamaterial possesses large quadratic nonlinearity and minimal cubic (Kerr-like) nonlinearity. This property allows phase matching and exponential power gain in a wide frequency range. The proof-of-principle measurements performed at temperature T = 4.2 K on Nb trilayer samples have demonstrated the validity of our concept of a practical Josephson parametric amplifier with great promise for quantum-limited performance.
Metamaterials are artificially designed materials to exhibit properties not available in natural materials by engineering the constituting elements at sub-wavelength scales, enabling unique interactions of matter with electromagnetic waves or coupling modes of electromagnetic waves. Examples of such novel optics phenomenons include negative index of refraction, cloaking, and super-resolution imaging. The study of superconducting metamaterials operating in the microwave frequency domain has recently generated significant interest in the framework of quantum technologies due to a wide range of direct applications, e.g., exploration of novel quantum optics phenomena, non-destructive quantum sensing, quantum-limited amplification, quantum information processing, and quantum illumination. In contrast to their normal metal and semiconducting counterparts, superconducting metamaterials offer some unique advantages. The most relevant of these for Josephson junction based metamaterials are low losses, flux quantization, and Josephson effects. The Josephson effect in a superconducting loop can also be exploited to exact more control over the nonlinearities of the meta-material.In this thesis, we present Josephson junction based metamaterials with in-situ tunability of second and third-order (Kerr) nonlinearities. We optimized the Josephson junction composites SNAILs, well-known in the superconducting circuits community, for the specific use case of building blocks for an impedance-matched nonlinear meta-material. In such devices, the strong third-order (Kerr) nonlinearity can be tuned from positive to negative values. To demonstrate the efficacy of this phenomenon, we have shown a use case of the meta-material as a TWPA with a new phase-matching mechanism: reversed Kerr phase matching, which utilizes the sign reversal of the Kerr nonlinearity to correct for the dispersion curvature of such devices arising due to its finite plasma. The meta-material operated as reversed Kerr TWPA exhibits up to 4 GHz wide combined amplification band with 8 GHz dynamic band tunability, -98 dBm saturation (1 dB compression point) around 20 dB gain, and amplifier added noise close to the standard quantum limit. The absence of any gaps in the transmission can provide a continuous amplification band with significantly lower gain ripples in contrast to the previously demonstrated TWPAs with dispersion engineering.We also present the generation of entanglement utilizing the metamaterials to demonstrate their versatility and further emphasize their potential in the general framework of nonlinear microwave quantum optics. Due to their large bandwidth, these devices have been identified as promising for generating two-mode squeezing and broadband entanglement. With a device optimized for the generation of broadband entanglement, we observed entanglement between two modes separated by up to 400 MHz. We measured logarithmic negativity between 0.27 and 0.51, and the collective quadrature squeezing below the vacuum limit between 1.5 and 2.1 dB. The presented proof-of-principle results can pave the way towards the implementation of Josephson junction based metamaterials in novel applications, including non-destructive single-photon detection, single-photon measurement and control in c-QED, photon-based quantum computing, precision sensing, the detection of dark matter, and quantum illumination.
Parametric amplification is essential for quantum measurement, enabling the amplification of weak microwave signals with minimal added noise. While Josephson-junction-based amplifiers have become standard in superconducting quantum circuits, their magnetic sensitivity, limited saturation power, and sub-kelvin operating requirements motivate the development of alternative nonlinear platforms. Here we demonstrate a two-mode kinetic-inductance parametric amplifier based on a pair of capacitively coupled Kerr-nonlinear resonators fabricated from NbTiN and NbN thin films. The distributed Kerr nonlinearity of these materials enables nondegenerate four-wave-mixing amplification with gains approaching 40 dB, gain-bandwidth products up to 6.9 MHz, and 1-dB compression powers two to three orders of magnitude higher than those of state-of-the-art Josephson amplifiers. A coupled-mode theoretical model accurately captures the pump-induced modification of the hybridized modes and quantitatively reproduces the observed signal and idler responses. The NbN device exhibits a significantly larger Kerr coefficient and superior gain-bandwidth performance, highlighting the advantages of high-kinetic-inductance materials. Our results establish coupled kinetic-inductance resonators as a robust platform for broadband, high-power, and magnetically resilient quantum-limited amplification, offering a scalable route for advanced readout in superconducting qubits, spin ensembles, quantum dots, and other microwave-quantum technologies.
A requirement for quantum information experiments using superconducting quantum circuits is the readout of extremely weak microwave signals. Quantum limited amplifiers are essential for such task and this is precisely why they occupy an always-growing importance in such experiments, particularly for superconducting quantum bits readout.In this thesis, we present two quantum limited amplifiers architectures: the first one is based on a resonator while the second one leverages a traveling-wave construction. These amplifiers both take advantage of tunable Josephson junctions (squid). It is the ideal component for quantum limited parametric amplification: it is both nonlinear and dissipationless (given its superconducting nature). This thesis demonstrates the operation of these Josephson quantum limited amplifiers and how they go beyond the state-of-the-art thanks to original design choices.An important limitation of resonant Josephson parametric amplifiers is their poor dynamic range. We identified the Kerr nonlinearity as the main cause, and we successfully managed to tailor it using Josephson junction arrays. We also developed a model in good agreement with the experimental data, therefore validating our initial assumption that the Kerr nonlinearity and saturation are linked. However, most of the resonant Josephson parametric amplifiers suffer from a fundamental issue, arising from their architecture. It is the conservation of the gain bandwidth product, therefore limiting their bandwidth. Traveling-wave architectures are well suited to overcome this limitation. However, two new issues must be dealt with: impedance matching and phase matching. To tackle the former, we developed an original and simple fabrication process in order to obtain a 50ohm matched 2000 squid array. As for the phase, we matched it by periodically modulating the impedance of the squid transmission line in order to open a photonic band gap. Therefore, we locally distort the dispersion relation. This step does not add any complexity to the initial fabrication process. Moreover, we developed a model in good agreement with experimental data while considering the nonlinear behavior of the photonic gap in a Josephson metamaterial. In addition to demonstrating high performance amplifiers poised for numerous quantum technological applications, this thesis opens the door to more fundamental quantum optics experiments taking advantage of these highly nonlinear transmission lines.With the resonant amplifiers, we measured a 1dB compression point around -117dBm and 45MHz bandwidth (at 20 db gain). With the traveling-wave amplifiers, we measured 18dB gain on a 2.25GHz bandwidth, a 1dB compression point reaching -103dBm and near quantum-limited noise performances.
The optical Kerr effect, in which a medium's refractive index is affected by the intensity of the transmitted light, is exploited not only in conventional optics, but also in superconducting circuits. This article reports a Josephson-junction-based metamaterial with a widely tunable Kerr constant that can even change sign. Controlled by an external magnetic field, this material can speed up or slow down the phase velocity of light per the intensity of the propagating electromagnetic wave. Such an engineered medium could be used for phase matching in traveling-wave parametric amplifiers, or in superconducting hardware for encoding or reading out quantum information.
Nearly quantum limited Josephson parametric amplifiers (JPAs) are essential components in superconducting quantum circuits. However, higher order nonlinearities of the Josephson cosine potential are known to cause gain compression, therefore limiting scalability. In an effort to reduce the fourth order, or Kerr nonlinearity, we realize a parametric amplifier with an Al-InAs superconductor–semiconductor hybrid Josephson junction (JJ). We extract the Kerr nonlinearity of the Al-InAs JJ from two different devices and show that it is three orders of magnitude lower compared to an Al-AlOX junction with identical Josephson inductance. We then demonstrate a four-wave-mixing (4WM) parametric amplifier made with an Al-InAs junction that achieves more than 20 dB of gain and −119 dBm of compression power, which outperforms single resonant JPAs based on Al junctions.