One-dimensional Josephson waveguides have generated significant interest in the fields of quantum technology and superconducting quantum information because they allow complete control over wave dispersion and nonlinear interactions.A variety of Josephson waveguides have been proposed and realized in the recent years, with applications ranging from near quantum-limited broadband amplification to multi-mode entanglement generation and non-reciprocal signals transmission.This thesis explores parametric interactions and entanglement generation in a novel architecture of Josephson waveguide. The latter consists of a high-pass microwave network and realizes an artificial material showing left-handed wave dispersion (or equivalently negative refractive index). The left-handed dispersion, combined with the Josephson nonlinearity, enables for various parametric processes, ranging from self-phase-matched broadband amplification of co-propagating modes to amplification and mixing of waves propagating in opposite directions. The realization of such Josephson waveguide opens new avenues within the framework of Josephson traveling wave parametric amplifiers and converters.Beyond these classical nonlinear optical processes, negative index Josephson waveguide are also powerful tools to generate nonclassical states of light such as broadband two-mode vacuum squeezed states and spatially separated entangled photon pairs. Here, we report about the measurements of such quantum states with this novel Josephson waveguide architecture, opening new perspectives for quantum sensing and quantum radar and illumination protocols, and more generally for microwave applications requiring the routing of entangled photons in different directions.
One-dimensional Josephson waveguides have generated significant interest in the fields of quantum technology and superconducting quantum information because they allow complete control over wave dispersion and nonlinear interactions.A variety of Josephson waveguides have been proposed and realized in the recent years, with applications ranging from near quantum-limited broadband amplification to multi-mode entanglement generation and non-reciprocal signals transmission.This thesis explores parametric interactions and entanglement generation in a novel architecture of Josephson waveguide. The latter consists of a high-pass microwave network and realizes an artificial material showing left-handed wave dispersion (or equivalently negative refractive index). The left-handed dispersion, combined with the Josephson nonlinearity, enables for various parametric processes, ranging from self-phase-matched broadband amplification of co-propagating modes to amplification and mixing of waves propagating in opposite directions. The realization of such Josephson waveguide opens new avenues within the framework of Josephson traveling wave parametric amplifiers and converters.Beyond these classical nonlinear optical processes, negative index Josephson waveguide are also powerful tools to generate nonclassical states of light such as broadband two-mode vacuum squeezed states and spatially separated entangled photon pairs. Here, we report about the measurements of such quantum states with this novel Josephson waveguide architecture, opening new perspectives for quantum sensing and quantum radar and illumination protocols, and more generally for microwave applications requiring the routing of entangled photons in different directions.
Josephson traveling-wave parametric amplifiers (JTWPAs) are promising platforms for realizing broadband quantum-limited amplification of microwave signals. However, substantial gain in such systems is attainable only when strict constraints on phase matching of the signal, idler, and pump waves are satisfied---this is rendered particularly challenging in the presence of nonlinear effects, such as self- and cross-phase modulation, which scale with the intensity of propagating signals. In this work, we present a simple JTWPA based on ``left-handed'' (negative-index) nonlinear Josephson metamaterial, which has phase matching native to its design, precluding the need for any complicated circuit or dispersion engineering. The resultant efficiency of the four-wave-mixing process can implement gains in excess of 20 dB over few-gigahertz bandwidths with much shorter lines than previous implementations. Furthermore, the intrinsic phase matching considerably simplifies the JTWPA design and operation compared to the previous implementations based on ``right-handed'' (positive-index) Josephson metamaterials, making the proposed architecture particularly appealing for integration with large superconducting architectures. The left-handed Josephson transmission line introduced here constitutes an alternative modality in distributed Josephson circuits, and forms a crucial piece of the unified framework that can be used to inform the optimal design and operation of broadband microwave amplifiers.
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.
One of the primary requirements for superconducting quantum information processors is high-fidelity, quantum non-demolition qubit readout. In superconducting circuits, we perform measurements with quantum-limited microwave amplifiers. These amplifiers are based on microwave cavities and powered by Josephson-junction based nonlinearities, which we drive to parametrically modulate the circuit and generate gain. However, cavity-based amplifiers generally suffer from a fixed gain-bandwidth product, a limited dynamic range, and the absence of directionality, and so they must be operated with external lossy microwave commercial components such as circulators. Many of these limitations can be circumvented by combining multiple parametric processes in a few-mode device, in particular by combining parametric drives which produce gain and those which produce gainless photon conversion. By combining balanced gain and conversion processes between a pair of modes, we have demonstrated transmission-only, phase-sensitive, gain-bandwidth-free amplification. We have also used measurements of transmon qubits with this mode of amplification to demonstrate its practical utility. More, by combining multiple instances of imbalanced gain and conversion processes among three modes, we have realized devices with non-reciprocal, transmission-only amplification, matched ports, and a large, gain-independent bandwidth. One of the biggest challenges in tuning multiple parametric processes is both inherent and dynamically-generated higher order nonlinearities in the device, which shift mode frequencies and parametric coupling strengths with pump power, preventing accurate balancing of the parametric processes. These can be controlled through engineering the Hamiltonian of the nonlinear element, in this thesis either a linearly-shunted Josephson Ring Modulator or SNAIL (Superconducting Nonlinear Asymmetric Inductive eLements), which for certain applied flux values can minimize or even change the sign of higher-order even nonlinearities. Additionally, we have explored a range of circuit parameters, allowing us to also control the relative size of odd-order nonlinearities. We have developed a series of prototypes which implement these concepts, and have achieved both high-dynamic range singly pumped amplifiers, and a promising platform for multi-parametric devices. We conclude by presenting recent progress towards implementing multiple parametric schemes that generates a practical directional amplifier, and discuss the remaining obstacles to a truly ideal parametric amplifiers.
Josephson meta-materials have recently emerged as very promising platform for superconducting quantum science and technologies. Their distinguishing potential resides in ability to engineer them at sub-wavelength scales, which allows complete control over wave dispersion and nonlinear interaction. In this article we report a versatile Josephson transmission line with strong third order nonlinearity which can be tuned from positive to negative values, and suppressed second order non linearity. As an initial implementation of this multipurpose meta-material, we operate it to demonstrate reversed Kerr phase-matching mechanism in traveling wave parametric amplification. Compared to previous state of the art phase matching approaches, this reversed Kerr phase matching avoids the presence of gaps in transmission, can reduce gain ripples, and allows in situ tunability of the amplification band over an unprecedented wide range. Besides such notable advancements in the amplification performance with direct applications to superconducting quantum computing and generation of broadband squeezing, the in-situ tunability with sign reversal of the nonlinearity in traveling wave structures, with no counterpart in optics to the best of our knowledge, opens exciting experimental possibilities in the general framework of microwave quantum optics, single-photon detection and quantum limited amplification.
Quantum computers based on superconducting circuits are approaching quantum supremacy, which means they have the potential to perform specific tasks significantly faster than even the most powerful classical supercomputers. As a crucial component in the measurement chain, parametric amplifiers based on Josephson junctions are promising tools for the readout of superconducting qubits in the microwave range. In this contribution, we present a novel Lie algebra approach for modeling a Josephson junction-embedded traveling-wave parametric amplifier, characterized by a lossy dielectric substrate and nonlinear dispersion, and investigate the generation of entangled signal-idler photon pairs in a two-mode squeezed state.
The precise control, entanglement, and measurement of quantum systems are central challenges in realizing scalable quantum information processing. This dissertation investigates how parametric modulation and engineered nonlinearity can be harnessed to both manipulate and measure superconducting qubits with high fidelity. In one part, controlled parametric drives are used to generate entanglement between qubit pairs and employ their joint states as probes of environmental dynamics. This approach enables the exploration of the non-Markovian nature of quantum environments, revealing how memory effects influence qubit coherence and energy relaxation. In a separate but conceptually related study, the same principle of parametric driving is utilized to design and analyze quantum-limited amplifiers based on three-wave mixing in weakly nonlinear Josephson circuits. An amplifier with a higher coupling quality factor than conventional JPAs is employed, allowing the two modes of a parity-time (PT) symmetric dimer to be mapped onto the in-phase (I) and quadrature (Q) components of the Josephson parametric amplifier. This mapping enables controlled exploration of non-Hermitian dynamics and mode coalescence within the amplifier’s quadrature space, offering new insights into PT-symmetric behavior and quantum-limited detection. Collectively, these investigations unify the themes of parametric control, entanglement, and amplification, advancing the broader understanding of quantum measurement and open-system dynamics.