In-Situ Echo Suppression in JTWPAs: A CLASSIQ SDK Implementation Blueprint

[Jayaudaykmar26589]

The Idea discussed here is derived from the paper titled "Observation and mitigation of microwave echoes from dielectric defects in Josephson
traveling wave amplifiers".

The link to the paper is https://arxiv.org/pdf/2503.00190

1. Research Paper Overview

Target Paper:
“Observation and mitigation of microwave echoes from dielectric defects in Josephson traveling wave amplifiers” presents both an experimental observation of unwanted echo signals—stemming from microscopic two-level defects (TLS) in the amplifier’s dielectric layers—and a mitigation protocol (BLAST) that uses a high-power pulse to effectively “blind” the amplifier to these defects. The work combines detailed spectral diffusion models with pulse-sequence experiments (including Hahn echo and stimulated echo sequences) to quantify the effects of these dielectric defects on the amplifier’s performance.

2. Technical Approach Using CLASSIQ SDK

A. Modeling the Physical System

**JTWPA Representation:**
Model the Josephson Traveling Wave Parametric Amplifier as a network (chain) of Josephson junctions interleaved with parallel-plate capacitors. In the CLASSIQ SDK, this can be done by defining a circuit module that mimics the distributed nonlinear elements and capacitive loads.

**Defect (TLS) Modeling:**
Incorporate dielectric defects as an ensemble of two-level systems (TLS). Each TLS is characterized by a Hamiltonian of the form
H/ℏ = (Δ/2) σₓ + (Δ₀/2) σ_z
and their collective effect is captured via a spectral diffusion model. This model describes the echo decay and is used to relate the microscopic TLS dynamics to measurable quantities like T₁ and T₂.

B. Pulse Sequence and Signal Analysis

**Echo Sequence Implementation:**
Implement the standard two-pulse (Hahn echo) and three-pulse (stimulated echo) sequences. These sequences are essential for both probing the defect-induced echoes and extracting coherence times.

**BLAST Mitigation Strategy:**
Design an additional pulse module that sends a high-power BLAST tone concurrently with or just prior to the drive pulses. This pulse “reflects” the high-power excitation from the JTWPA, preventing the dielectric defects from being activated, as described in the paper.

**Simulation of Microwave Signals:**
Using CLASSIQ’s simulation capabilities, set up time-domain simulations where the input pulse sequence (including drive, pump, and BLAST pulses) is applied to the modeled JTWPA circuit. Monitor the output to measure echo amplitudes and assess the mitigation’s efficacy.

C. Parameter Calibration and Optimization

**Extracting Key Parameters:**
Calibrate simulation parameters (such as pulse amplitudes, durations, and delays) to replicate the echo dynamics (e.g., the coherence decay modeled by the spectral diffusion) reported in the paper.

**Iterative Optimization:**
Leverage CLASSIQ SDK’s optimization routines to adjust parameters such as the BLAST pulse timing and power, ensuring that the simulation recovers the low-power signal (i.e., the expected amplifier gain and noise characteristics) after mitigation.

Key Points about the points to be Demonstrated:

**Device and Defect Modeling:** The JTWPA device is built with embedded TLS defects to simulate dielectric echoes.
**Pulse Sequence Design:** Both standard Hahn echo and the BLAST mitigation pulse are defined.
Simulation and Data Extraction: The simulator runs the circuit under cryogenic conditions, and analysis routines extract echo amplitude and coherence parameters.

Summary:

Using the CLASSIQ SDK, the implementation strategy involves:

Identifying the Research Focus:
Implementing the experimental study on microwave echoes due to dielectric defects in JTWPAs as detailed in the target paper.

Developing a Technical Approach:
    Model the amplifier and incorporate TLS-based defect models.
    Implement pulse sequences (including echo sequences and the BLAST pulse for mitigation).
    Calibrate and optimize simulation parameters to match experimental observations.

High-Level Demonstration:
A modular pseudo-code example shows how to define the circuit, configure pulses, and simulate the echo response, demonstrating the key concepts from the paper.

This strategy not only allows for replicating the experimental findings in simulation but also provides a platform for further exploration and optimization of the mitigation protocols described in the paper.

[TomerGoldfriend]

Thank you @Jayaudaykmar26589 , what kind of quantum algorithm are you going to implement? How does the system described in the paper can be captured by a quantum model that eventually decomposes into a set of quantum gate-based circuit?