Broadband parametric amplifiers based on nonlinear kinetic inductance artificial transmission lines

Abstract

We present broadband parametric amplifiers based on the kinetic inductance of superconducting NbTiN thin films in an artificial (lumped-element) transmission line architecture. We demonstrate two amplifier designs implementing different phase matching techniques: periodic impedance loading, and resonator phase shifters placed periodically along the transmission line. Our design offers several advantages over previous CPW-based amplifiers, including intrinsic 50 ohm characteristic impedance, natural suppression of higher pump harmonics, lower required pump power, and shorter total trace length. Experimental realizations of both versions of the amplifiers are demonstrated. With a transmission line length of 20 cm, we have achieved gains of 15 dB over several GHz of bandwidth.Cryogenic low-noise broadband amplifiers are critical for a variety of applications, such as the multiplexed readout of astronomical detectors [1][2][3] and superconducting qubits [4][5][6], the manipulation of mechanical resonators coupled to microwave cavities [7], and the study of nonclassical states of microwave light [8,9]. These experiments often use high electron mobility transistor (HEMT) amplifiers, which typically have a noise temperature of 2-5 K in the 4-8 GHz range [10]. This noise is 10-40 times above the standard quantum limit, the fundamental limit imposed by quantum mechanics [11].Over the last decade, there has been rapid development of quantum-limited microwave amplifiers, including particularly Josephson parametric amplifiers (JPAs) [12][13][14]. JPAs use the dissipationless nonlinearity of Josephson junctions in a parametric process to achieve gain. Both narrowband JPAs, based on junction-embedded resonant architectures, and broadband JPAs, based on junction-embedded transmission lines, have been developed and have demonstrated near quantum-limited noise performance [15,16]. However, the ∼ 10 µA critical current of the junctions limits the dynamic range of these devices and excludes them from some important applications, such as the multiplexed readout of thousands of qubits or detectors. In addition, fabricating a large number (> 1000) of junctions with high yield is a nontrivial task.Recently, another type of broadband parametric amplifier based on the nonlinear kinetic inductance of NbTiN transmission lines has been proposed [17,18,[20][21][22]. These devices are simple to fabricate, requiring only one lithography step (patterning of the NbTiN film). Due to the 1 mA critical currents of the films, the amplifier saturation power is 5-6 orders of magnitude higher than JPAs, making them promising for readout of a large array of detectors or qubits. In contrast with reflectiontype resonant JPAs, the traveling-wave architecture of the NbTiN amplifier eliminates the need for a circulator, enabling on-chip integration with a detector or qubit. In previous work, NbTiN amplifiers were realized as long coplanar waveguide (CPW) transmission lines, with >20 dB gain over several GHz bandwidth [18]. Despite the excellent gain perform...

Wide-band parametric amplifier readout and resolution of optical microwave kinetic inductance detectors

“…the center line width and gaps are 320 nm). In order to lower the characteristic impedance to 50 Ω, added capacitance is provided with a interdigitated structure in a similar manner to the amplifier described by Chaudhuri et al 25 Additionally, the amplifier is operated in a three-wave mixing mode by applying a DC bias current using the technique shown by Vissers et al 27 Further details about this amplifier are in preparation and will be published separately.…”

Photonic-Crystal Josephson Traveling-Wave Parametric Amplifier

“…Also K-TWPA's require very high pump powers, which can cause unwanted heating effects [25]. These two limitations probably explain why this device and subsequent implementations [31][32][33][34][35] systematically showed noise close to but above the quantum limit.…”

Mesoscopic Hamiltonian for Josephson traveling-wave parametric amplifiers

“…As noted in section 2, the amplification process is most efficient if ∆Ω = 0. As will become clear from the quantum mechanical treatment of the problem in due course, ∆Ω corresponds to ∆K in equation (16). However, due to dispersion (equation (10)) and self-and cross-modulation (equation (11)) this term cannot be 0 in a transmission line embedded with Josephson junctions.…”

“…The resonators divide the structure in sections. Within each section, the evolution of the mode amplitudes follows equation (16) with the coupling constants as given by equations (11) and (12). Then, between two sections, one evaluates the transmission coefficient due to the presence of the resonator, updates the mode amplitudes accordingly and uses those amplitudes as input for the next section.…”