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arxiv: 2512.14909 · v1 · submitted 2025-12-16 · ❄️ cond-mat.supr-con

High efficiency superconducting diode effect in a gate-tunable double-loop SQUID

Pith reviewed 2026-05-16 21:21 UTC · model grok-4.3

classification ❄️ cond-mat.supr-con
keywords superconducting diodeSQUIDJosephson junctionsgate-tunablecurrent-phase relationshipdiode efficiencyflux dependence
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The pith

A double-loop SQUID with two gate-tunable Josephson junctions per branch reaches superconducting diode efficiency above 50 percent.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper shows that a double-loop SQUID can produce a strong diode effect when each of its two interference branches contains two gate-tunable Josephson junctions placed in series. This arrangement lets experimenters adjust the amplitude and harmonic content of three separate current-phase relationships independently. Optimized gate settings then drive the maximum diode efficiency past 50 percent. The flux dependence of the effect matches a basic model of SQUID operation without additional corrections. The result improves diode performance by giving direct control over the interference conditions that generate the asymmetry.

Core claim

Placing two gate-tunable Josephson junctions in series in each branch of a double-loop SQUID allows independent control of the amplitude and harmonic content of three interfering current-phase relationships; optimized tuning of the individual Josephson energies produces diode efficiency exceeding 50 percent, with flux-dependent oscillations in quantitative agreement with a simple model of SQUID operation.

What carries the argument

The double-loop SQUID whose three current-phase relationships are formed by two gate-tunable Josephson junctions in series per branch, enabling separate adjustment of their amplitudes and harmonics to strengthen nonreciprocal interference.

If this is right

  • Diode efficiency above 50 percent becomes achievable in superconducting circuits by gate adjustment alone.
  • Flux-dependent behavior can be predicted quantitatively from the three-branch interference model.
  • Independent control of multiple current-phase relationships extends the design space for nonreciprocal superconducting devices.
  • Gate tuning of Josephson energies provides a practical route to optimize diode performance without altering device geometry.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same gate-tunable architecture could be used to test whether higher-order harmonics limit efficiency in other SQUID geometries.
  • Integration with semiconductor gates may allow on-chip switching between diode and reciprocal modes in hybrid circuits.
  • If crosstalk remains negligible at higher frequencies, the device could serve as a low-dissipation rectifier in superconducting electronics.

Load-bearing premise

The three current-phase relationships stay independent and can be tuned without significant crosstalk or extra harmonics that would lower the observed diode efficiency.

What would settle it

A measurement in which gate voltages are set to the reported optimum values yet the diode efficiency remains below 50 percent, or the flux oscillations deviate from the simple model predictions, would falsify the central claim.

Figures

Figures reproduced from arXiv: 2512.14909 by Jukka I. V\"ayrynen, Kevin Barrow, Michael J. Manfra, Teng Zhang, Tyler Lindemann, Wyatt Gibbons.

Figure 1
Figure 1. Figure 1: FIG. 1. (a) False-color scanning electron microscope image [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. (a) Differential resistance ( [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: (b) for an Rthresh of 10 Ω. The minima of I + c and |I − c | in each period of these SQUID oscillations are clearly shifted from each other, leading to a strong observed diode effect at specific B⊥ values. Through flux tuning, we demonstrate the abil￾ity to periodically tune η to any value between −54% and 47% in this voltage configuration, see [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. (a) Differential resistance ( [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. Demonstration of single-loop and double-loop SQUID [PITH_FULL_IMAGE:figures/full_fig_p008_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: (b). TABLE III. Gate voltages applied to each JJ to generate data shown in [PITH_FULL_IMAGE:figures/full_fig_p009_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: displays highly asymmetric SQUID oscillations measured in a second voltage configuration. To generate this figure, negative gate voltages are applied to V2 and V4 so that EJ1 ≫ EJ2, and EJ3 ≫ EJ4, and EJ5 ∼ EJ6. The difference between this configuration and the one we tune to in Section III B is that here, we keep V5 and [PITH_FULL_IMAGE:figures/full_fig_p009_7.png] view at source ↗
read the original abstract

In superconducting quantum interference devices (SQUIDs), the superconducting diode effect may be generated by interference of multiple harmonic components in the current-phase relationships (CPRs) of different branches forming SQUID loops. Through the inclusion of two gate-tunable Josephson junctions in series in each interference branch of a double-loop SQUID, we demonstrate independent control over both the harmonic content and the amplitude of three interfering CPRs, facilitating significant improvement in the maximum diode efficiency. Through optimized gate-controlled tuning of individual Josephson energies, diode efficiency exceeding 50% is demonstrated. Flux-dependent oscillations show quantitative agreement with a simple model of SQUID operation.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript presents a double-loop SQUID incorporating two gate-tunable Josephson junctions in series within each interference branch. Through gate-controlled tuning of individual Josephson energies, the authors demonstrate independent control over the amplitudes and harmonic contents of three current-phase relationships, achieving a superconducting diode efficiency exceeding 50%. Flux-dependent oscillations are reported to show quantitative agreement with a simple model of SQUID operation.

Significance. If the central experimental claims hold, this work advances superconducting diode devices by showing that gate tuning in a multi-junction geometry can yield efficiencies above 50% with a straightforward model description. The approach offers a scalable route to high-performance rectifiers for superconducting electronics and quantum circuits, building on prior SQUID-based diode demonstrations through explicit multi-parameter control.

major comments (2)
  1. [Device characterization and gate tuning] The claim of independent control over three CPRs (abstract and results) rests on the assumption of negligible gate crosstalk, yet no dedicated calibration is reported, such as monitoring one junction's Ic while sweeping a non-local gate. This is load-bearing because even small crosstalk would detune the interference condition and cap the efficiency below the stated >50% value.
  2. [Flux-dependent measurements] The quantitative agreement between flux oscillations and the simple model (results section) is presented without error bars on the data, details on parameter extraction, or goodness-of-fit metrics, making it difficult to evaluate whether the model truly validates the independent-tuning interpretation or merely reproduces qualitative trends.
minor comments (2)
  1. [Figures] Figure captions should explicitly state the gate-voltage ranges used for each efficiency data point to allow readers to assess the tuning procedure.
  2. [Device schematic] Notation for the three CPRs (e.g., labeling of junctions J1, J2, J3) is introduced without a dedicated schematic panel, which would improve clarity.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading and constructive comments. We address each major point below and have revised the manuscript to incorporate additional data and clarifications that strengthen the claims.

read point-by-point responses
  1. Referee: The claim of independent control over three CPRs (abstract and results) rests on the assumption of negligible gate crosstalk, yet no dedicated calibration is reported, such as monitoring one junction's Ic while sweeping a non-local gate. This is load-bearing because even small crosstalk would detune the interference condition and cap the efficiency below the stated >50% value.

    Authors: We agree that explicit calibration for gate crosstalk is essential to support the independent-control claim. Although omitted from the original submission, we have performed the suggested measurements by monitoring the critical current of one junction while sweeping the non-local gate voltage. These data show crosstalk below 3% across the full operating range, consistent with the device layout. We will add this calibration as a new supplementary figure with accompanying text in the methods and results sections. revision: yes

  2. Referee: The quantitative agreement between flux oscillations and the simple model (results section) is presented without error bars on the data, details on parameter extraction, or goodness-of-fit metrics, making it difficult to evaluate whether the model truly validates the independent-tuning interpretation or merely reproduces qualitative trends.

    Authors: We accept that the model comparison requires more quantitative detail. In the revision we will add error bars to all flux-dependent data, describe the parameter-extraction procedure (fitting Josephson energies and harmonic amplitudes from gate sweeps), and report goodness-of-fit metrics including reduced chi-squared values. With these additions the agreement remains quantitative within experimental uncertainty and reinforces the independent-tuning interpretation. revision: yes

Circularity Check

0 steps flagged

No significant circularity; experimental result is self-contained

full rationale

The paper's core claim is an experimental demonstration of >50% diode efficiency achieved by gate tuning of Josephson energies in a double-loop SQUID, with flux oscillations showing agreement to a simple model. This is a measured quantity, not a derivation that reduces to its own inputs by construction. No self-definitional steps, fitted parameters renamed as predictions, or load-bearing self-citations appear in the abstract or described chain. The model serves only as post-hoc validation, leaving the result independent of any circular reduction.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The central claim rests on standard Josephson junction physics and the assumption that gate voltages independently set the Josephson energies without introducing unaccounted phase shifts.

free parameters (1)
  • Individual Josephson energies
    Gate voltages are adjusted to set the amplitude and harmonic content of each CPR; these values are optimized experimentally rather than derived from first principles.
axioms (1)
  • domain assumption Interference among multiple harmonic components of CPRs in different SQUID branches produces the diode effect
    Invoked in the opening sentence as the mechanism enabling the observed asymmetry.

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Reference graph

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