Session S38: Superconducting Wideband and Traveling-wave Parametric Amplifiers

Novel superconductor-semiconductor low-noise amplifier based on InAs-Al JJFET

Low-noise amplifiers (LNAs) based on traditional III-V semiconductor transistors can achieve many gigahertz of bandwidth and milliwatts of compression power. However, they miss the quantum-limit by an order of magnitude, making them too noisy to directly amplify the signal from superconducting qubit processors. Recently, Josephson Junction Field Effect Transistors (JJFETs) made from InAs-Al superconductor-semiconductor heterostructures have shown promise for building quantum circuits, thanks to their high carrier mobility and the tunability of their supercurrent. Given this new platform which combines the properties of semiconductors and superconductors, we propose that it is a potential candidate for building quantum-limited LNAs, like the well-developed Josephson parametric amplifiers. We will discuss the circuit design, numerical simulation, fabrication, and preliminary experiments on cryogenic LNAs based on InAs-Al JJFETs.   

Fabrication and characterization of Josephson parametric amplifiers based on micron-scale Josephson junctions

Josephson parametric amplifiers (JPAs) with quantum limited noise performance have become essential components in superconducting quantum circuits. We describe a fabrication process to yield micrometer-scale Josephson junctions [1].  The room temperature characterization of junctions will be presented as a function of oxidation dose and junction geometry. Low temperature current-voltage characteristics indicate that our fabrication process yields high quality junctions. Next, we design and fabricate JPAs. Our fabrication process yields low loss frequency tunable JPAs with typical gain of ~30 dB. The noise characterization of our JPAs reveal near quantum limited noise performance. This material  is based upon work supported by the U.S. Department of Energy, Office of Science, National Quantum  Information Science Research Centers, Superconducting Quantum Materials and Systems Center (SQMS) under contract number DE-AC02-07CH11359.

[1] M. Bal et al.,  “Overlap junctions for superconducting quantum electronics and amplifiers”, Appl. Phys. Lett. 118, 112601 (2021)   

Toward the near-quantum-limited multiplexed readout of hundreds of resonators with a KI-TWPA

As the number of qubits in quantum computers continues to increase, their readout architecture will face the same technical challenge as arrays of transition-edge sensors and microwave kinetic inductance detectors: namely, what is a scalable solution for the quantum-limited readout of hundreds and thousands of frequency-multiplexed resonators? For both qubit and sensor applications, the cooling power required to brute-force scale the existing cryogenic semiconductor amplifier technology is a major obstacle. In this context, traveling-wave parametric amplifiers (TWPAs) have emerged as a more power-efficient solution [1], with nearly quantum-limited noise performance. In this talk, I will discuss the design and characterization of highly scalable readout architectures leveraging TWPAs, and will present our efforts to measure an array of 64 nonlinear resonators with a kinetic-inductance TWPA, whose added noise approaches the quantum limit.

 

[1]: arXiv: 2110.08142 (2021)   

Traveling Wave Parametric Amplification without Dispersion Engineering

Josephson Traveling Wave Parametric Amplifiers (J-TWPAs) are promising platforms for realizing quantum-limited broadband amplification of microwave signals. However, substantial gain in such systems is attainable only when strict constraints on phase matching 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 pump intensity. A recent notable approach to alleviate this problem involves introducing resonant elements into the transmission line and pumping near the stop band of the modified dispersion curve. Here we propose a new system that can realize large broadband gain without employing any dispersion engineering. The efficiency of the resultant four-wave mixing process allows achieving >20dB gain over few-GHz bandwidths, with much shorter lines than previous implementations, making the proposed architecture particularly appealing from a fabrication perspective. Additional optimization, coupled with flexibility in pump engineering, can be used to modify the gain profile in view of targeted applications, such as optimizing maximum gain vs constant-gain bandwidth.   

Low-loss Traveling-Wave Parametric Amplifier without Dispersion Engineering

We discuss theoretical and experimental results about a novel architecture of Traveling-Wave Amplifier (TWPA), based on an array of coupled asymmetric SQUIDs which allows for phase matching a four-wave mixing process for efficient parametric amplification. Unique to this design is that the nonlinear 3rd order term in the energy phase relation is suppressed as the 4th order Kerr coefficient can be tuned with a magnetic flux over a wide range and even change sign. The change in sign of the Kerr non-linearity can be exploited along with the chromatic dispersion of the TWPA for phase matching of a four-wave mixing process without the need for introducing dispersion engineering resonant elements which prohibit a tunable pump frequency, introduce gain ripples, and result in a stop-band in the middle of the gain bandwidth. The design allows for tunability of the characteristic impedance of the TWPA as well as reduced sensitivity of amplifier performance to fabrication tolerances in Josephson junctions. We will present preliminary results of TWPAs fabricated with low-loss dielectrics which show low insertion loss, sufficient gain, wide bandwidth and discuss pump depletion effects due to the generation of higher harmonics.   

Josephson meta-materials with tunable non-linearities and traveling wave parametric amplification

Josephson meta-materials have recently emerged as very promising platform for novel quantum optics experiments in microwave domain. Engineering them at sub-wavelength scales can allow complete control over wave dispersion and non-linear interactions.

We will discuss experimental realization of a broadband non-linear Josephson meta-material composed of an array of superconducting non-linear asymmetric inductive elements (SNAILs). The asymmetry in the SNAILs allows tuning and sign reversal of the Kerr and second order non-linearity by applying an external magnetic flux. The sign reversal of non-linearities at sub wavelength scales can also be utilized for their suppression. We will present use case of such devices as a near quantum limited broadband amplifier and discuss perspectives.   

Three-wave mixing Josephson traveling wave parametric amplifiers at 750 MHz and 1500 MHz

We present our latest results on Josephson traveling wave parametric amplifiers (TWPAs), which are currently in fabrication with our Nb/Al-AlO_x/Nb junction process. As a follow-up of our successful 4-9 GHz demonstrator operating in three-wave mixing, we are pursuing the adaptation of the TWPA concept to lower radio frequency bands. The motivation is to extend the application area to, e.g., spin qubit quantum computing. The device design features superconducting nonlinear asymmetric inductive elements (SNAILs), and an integrated on-chip magnetic flux bias line. We will discuss how we approach some specific low-frequency challenges such as control over footprint and engineered dispersion.   

Three wave mixing Josephson traveling wave parametric amplifier featuring SNAIL for cQED frequency range

We present our latest experimental results on Josephson traveling wave parametric amplifiers (TWPAs) fabricated with our Nb/Al-AlO_x/Nb junction process [1]. The amplifier has demonstrated broadband gain in excess of 14 dB and maximum added noise of 2 photon between 4 to 8 GHz. We will discuss dispersion engineering employed in the device design and noise measurement results for the amplifier performed using a cryogenic noise source [2]. As a use case, we present measurements of superconducting resonators where a typical TWPA reduces the measurement time significantly without requiring retuning of the TWPA for different samples in subsequent cooldowns.

[1] Leif Grönberg et al., Superconductor Science and Technology 30, 125016 (2017)

[2] Simbierowicz, Slawomir et al., Review of Scientific Instruments 92.3 (2021), 034708.   

Traveling wave parametric amplifiers for microwave quantum optics (PART I)

Traveling wave parametric amplifiers (TWPAs) have proven to be key tools to realize broadband amplification near the quantum limit. However, their range of application is not limited to signal amplification. They are even promising candidates for multi-mode entanglement generation to realize quantum optics experiments in the microwave regime. We will present the experimental operation of a Josephson TWPA as a source of two-mode squeezed microwave radiation, demonstrating broadband entanglement generation and discuss the perspectives of this result.   

Traveling wave parametric amplifiers for microwave quantum optics (PART II)

Traveling wave parametric amplifiers (TWPAs) have proven to be key tools to realize broadband amplification near the quantum limit. However, their range of application is not limited to signal amplification. They are even promising candidates for multi-mode entanglement generation to realize quantum optics experiments in the microwave regime. In this context, one quickly reaches parameter regimes where higher harmonics of the pump field build up and influence the device performance crucially. Hence, a theoretical description capturing the impact of these higher harmonics becomes indispensable. To study the influence of these higher harmonics, we extend the standard description of signal and idler mode dynamics in the TWPA accordingly. Based on our model we explore the effects of higher harmonics on gain, noise and entanglement characteristics, and compare our results to experimental data.   

A topological Josephson traveling wave parametric amplifier

We show how to realize a topological traveling wave parametric amplifier with a chain of Josephson junctions and four-wave mixing. The amplifier manifests directional and near quantum-limited amplification of microwave signals with a gain that grows exponentially with the chain size while keeping the bandwidth constant. We show that the directional amplification has a topological origin and therefore does not require any engineering to maintain phase matching along the chain, and it is moreover resilient to disorder. This Josephson topological amplifier can be immediately implemented with state-of-the-art superconducting technology, opening up a new route for the efficient detection of microwave quantum signals.   

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This work presents the latest refinements of our fabrication process for Nb/Al-AlO_x/Nb Josephson junctions. A key element is a side-wall spacer passivated structure, which is effective in the formation of junctions with sizes down to the sub-micrometer range. The multi-layer process is carried out on 150 mm wafers with UV lithography.  Critical current density tuning is achieved in the range of 0.1-3 kA cm^-2, which supports a multitude of applications.  We are continuously validating the process quality by characterizing cryogenic devices with relevance for quantum computing. These include Josephson parametric amplifiers including traveling wave parametric amplifiers, Josephson oscillators, and an emerging category of single-flux quantum circuits