Post-fabrication frequency trimming of coplanar-waveguide resonators in circuit QED quantum processors

Abstract

We present the use of a set of airbridges to trim the frequency of microwave coplanar-waveguide (CPW) resonators post-fabrication. This method is compatible with the fabrication steps of conventional CPW airbridges and crossovers and increases device yield by allowing compensation of design and fabrication uncertainty with 100 MHz range and 10 MHz resolution. We showcase two applications in circuit QED. The first is the elimination of frequency collisions between resonators intended to readout different transmons by frequency-division multiplexing. The second is frequency matching of readout and Purcell-filter resonator pairs. Combining this matching with transmon frequency trimming by laser annealing reliably achieves fast and high-fidelity readout across 17-transmon quantum processors.

Wafer-scale uniformity of Dolan-bridge and bridgeless Manhattan-style Josephson junctions for superconducting quantum processors

“…In the Planar 17Q wafer, a 13 × 13 mm die-level layout mimicking our planar 17-qubit SQP (Surface-17 [11,21,29]) is copy-pasted into two 2 × 4 arrays. The top half of the wafer has test-structure arrays for Dolan-bridge JJs, while the bottom half has test-structure arrays for Manhattan-style JJs.…”

“…At the location of each transmon of the SQP, we place a sub-array of 4 × 4 test structures. Within each sub-array (figure 1(b)), the designed single-junction overlap area (A overlap ) is finely stepped within one of three ranges, labeled low (l), mid (m) and high (h), mimicking the choice of three qubit-frequency groups in our SQPs [11,16,21,29]. For Dolan-bridge JJs, we change A overlap by varying the width W t of the top electrode and keeping the width of the bottom electrode W b = 3W t .…”

“…It also increases residual ZZ coupling in processors with always-on qubit-qubit coupling [2,3,16], making gate fidelity and leakage dependent on the state of spectator qubits [17]. Laser annealing of qubit Josephson junctions (JJs) [15,[18][19][20][21] is an established method for selective qubit frequency trimming without intrinsic effect on qubit coherence. Currently, laser annealing allows a monotonic decrease with ∼300 MHz range and ∼15 MHz imprecision (defined as the standard deviation of frequency targeting error post-annealing) [21].…”

“…Laser annealing of qubit Josephson junctions (JJs) [15,[18][19][20][21] is an established method for selective qubit frequency trimming without intrinsic effect on qubit coherence. Currently, laser annealing allows a monotonic decrease with ∼300 MHz range and ∼15 MHz imprecision (defined as the standard deviation of frequency targeting error post-annealing) [21]. To safely rely on laser annealing for post-fabrication trimming, fabrication itself must achieve an imprecision several times lower than the tuning range, e.g.…”

Optimize Purcell filter design for reducing influence of fabrication variation

“…Recently, researchers used a set of air bridges to adjust the frequency of the CPW resonator, achieving frequency matching between the readout resonator and the Purcell filter. [21] To avoid trials and errors in experiments, this work combines the circuit simulations and the finite element calculations to analyze the microwave transmission characteristics and coupling structure design of the Purcell filter (Heinsoo et al [20] ) under graphical edge etching deviations. This study provides design guidance for optimizing the structure of the CPW, filters, and feed lines, so as to significantly improve the performance stability of the Purcell filter.…”