Flux-driven Josephson parametric amplifier

Abstract

We have developed a Josephson parametric amplifier, comprising a superconducting coplanar waveguide resonator terminated by a dc SQUID (superconducting quantum interference device). An external field (the pump, ∼ 20 GHz) modulates the flux threading the dc SQUID, and, thereby, the resonant frequency of the cavity field (the signal, ∼ 10 GHz), which leads to parametric signal amplification. We operated the amplifier at different band centers, and observed amplification (17 dB at maximum) and deamplification depending on the relative phase between the pump and the signal. The noise temperature is estimated to be less than 0.87 K.Degenerate parametric amplifiers are phase sensitive amplifiers, which can in principle amplify one of the two quadratures of a signal without introducing extra noise. 1,2 Parametric amplifiers based on the nonlinear inductance of a Josephson junction have been studied for a long time, 3 including one which demonstrated vacuum noise squeezing. 4 Recently, there has been a renewed interest in parametric amplifiers 5,6,7 due in part to the increasing need for quantum-limited amplification in the field of quantum information processing using superconducting circuits. 8,9 In the present work, we design a Josephson parametric amplifier, comprising a superconducting transmissionline resonator terminated by a dc SQUID (superconducting quantum interference device). Contrary to the previous works, the pump is not used to directly modulate a current through the Josephson junction, but is instead used to modulate a flux through the dc SQUID. 10 The resonant frequency of the resonator, namely, the band center of the signal, is widely controllable by a dc flux also applied to the SQUID (see also Ref. [7]). Moreover, as the pump and the signal are applied to different ports and their frequencies are twice different (see below), it is straightforward to separate the output signal from the pump. This is a unique property of the fluxpumping scheme; it arises because the finite dc flux bias allows linear coupling of the pump even in the absence of a dc current bias across the SQUID. 11 We operated such a flux-driven parametric amplifier and characterized its basic properties. Figure 1a shows a schematic diagram of the flux-driven parametric amplifier. The primary component of the amplifier is a transmission-line resonator defined by its coupling capacitance C c and a dc SQUID termination. The magnetic flux Φ penetrating the SQUID loop changes the boundary condition of the resonator at the right end (by the change of the Josephson inductance), and hence enables us to control the resonant frequency. 12,13 The resonant frequency f 0 for the first mode (λ/4 ≥ d, where λ is the wavelength and d is the cavity length) is schematically drawn as a function of Φ/Φ 0 in Fig. 1b, where Φ 0 is a flux quantum (see also Fig. 2a). We now assume the cavity resonance is set to a particular value, f 0dc , by applying a dc flux Φ dc (open circle in the figure). We then apply microwaves at a frequency 2f 0dc to the pump line wh...

Effect of Higher-Order Nonlinearities on Amplification and Squeezing in Josephson Parametric Amplifiers

“…With this slight modification of the circuit, parametric amplification can be obtained by flux-pumping. This pumping scheme has been extensively studied both experimentally [5,36,50] and theoretically [35]. Here, we derive the Hamiltonian of the flux-pumped JPA similarly to Ref.…”

“…This empirical value of κ is lower than expected from the lumped-element capacitance; we attribute this difference to spatial impedance variations in the JPA environment [10]. The SQUID is flux-pumped to provide up to 25 dB of gain using an on-chip bias line [5] and the device is mounted with a 180 • hybrid launch to reject common mode noise. The amplifier is shielded by an aluminum box and mounted at the base plate of a dilution refrigerator (∼ 20 mK).…”

“…Following the path of Yurke's et al work in the late 1980s [1][2][3], several designs of Josephson junction-based parametric amplifiers (JPAs) have been introduced [4][5][6][7][8][9][10][11]. In addition to high-fidelity superconducting qubit readout leading to the observation of quantum jumps [12,13], this new generation of near quantumlimited amplifiers have opened up new experimental possibilities such as the creation and tomography of squeezed microwave light [14][15][16], and detailed weak measurement experiments [17][18][19].…”

“…We derive the corrections to the JPA Hamiltonian for the single-mode and single-port lumped-element JPA [7,25]. Using the formalism of quantum optics, we compare three frequently used pumping schemes of the JPA: monochromatic current pump [7,33], bichromatic current pump [34], and monochromatic flux pump [5,35,36]. We derive the leading higher-order corrections for each and study numerically their effect on gain, quantum efficiency, squeezing level and gaussianity of the output field.…”

Nondegenerate parametric oscillations in a tunable superconducting resonator

“…A typical cQED parametric device consists of a high-quality superconducting resonator integrated with Josephson elements that induce a Kerr nonlinearity in the resonator and also allow for rapid modulation of the resonator frequency [8][9][10][11].…”