SequentialMeasurements.jl

A Julia package for simulating noisy quantum systems under sequential measurements with dynamical decoupling control. The package builds upon QuantumOptics.jl for time-dependent quantum evolution and operator manipulation.

Features

• Simulation of quantum systems with configurable number of bath qubits
• Support for different noise models through customizable power spectral density functions
• Implementation of Concatenated Dynamical Decoupling (CDD) sequences
• Flexible measurement schemes (fidelity measurements, expectation values)
• Parallel execution support for multiple realizations
• Data management and persistence capabilities

Dependencies

The package primarily depends on:

• QuantumOptics.jl: Provides the core functionality for quantum operations and time-dependent evolution
• Other standard Julia packages for numerical computations and data handling

Installation

To install the package for development:

julia> using Pkg
julia> Pkg.develop(url="https://github.com/diego-bernal/SequentialMeasurements.jl.git")

Usage Example

Here's a basic example of running an error virtualization simulation:

using SequentialMeasurements

# Define control parameters
ctrl_params_dict = Dict(
    :n => 0,           # CDD order
    :t0 => 0.0,       # initial time
    :τg => 1.0,       # gate duration
    :nsteps => 10,    # time steps per evolution
    :M_max => 60      # control cycles
)

# Define noise parameters
noise_params_dict = Dict(
    :Nb => 0,                             # number of bath qubits (0 for classical noise)
    :psd_function => lf_gaussian,         # spectral density function
    :psd_kwargs => Dict(:s => 1.0, :Δ0 => 50, :Γ0 => 0.1),
    :ωu => 2π*1.0,                       # upper frequency cutoff
    :Nh => Int(2.0^12)                   # number of harmonics
)

# Define measurement scheme
measurement_scheme_dict = Dict(
    :fout => process_fidelity_with_plus,  # measurement processing function
    :conditional_evolution => false        # whether to use conditional evolution
)

# Initialize components
control = initialize_ctrl(:cdd, ctrl_params_dict)
noise = initialize_noise(:lf_gaussian, noise_params_dict)
measurement_scheme = initialize_measurement_scheme(measurement_scheme_dict)

# Run simulation
results = run_simulation(
    1000,                                 # number of realizations
    noise,
    control,
    "output_directory",                   # data collection path
    measurement_scheme,
    error_virtualization_realization;     # realization function 
    save_output=false                     # whether to save results to disk
)

Available Measurement Options

The package provides several measurement processing functions:

• process_fidelity_with_plus: Measures fidelity with respect to the |+⟩ state
• process_fidelity: Generic fidelity measurement with respect to any target state
• process_expectation: Measures expectation value of an operator

Measurements can be performed in two modes:

• Unconditional evolution (conditional_evolution = false): Average over all possible measurement outcomes
• Conditional evolution (conditional_evolution = true): Perform measurements and update states based on outcomes

Noise Models

The package includes several built-in spectral density functions:

• lf_gaussian: Low-frequency Gaussian noise
• hf_gaussian: High-frequency Gaussian noise
• lorentzian: Lorentzian spectral density
• lorentzian_article: Alternative Lorentzian parameterization

You can also implement custom spectral density functions for specific noise models.

Contributing

Contributions are welcome! Here's how you can help:

1. Fork the repository
2. Create a new branch (git checkout -b feature/your-feature)
3. Make your changes
4. Run the tests (julia> ]test SequentialMeasurements)
5. Commit your changes (git commit -am 'Add some feature')
6. Push to the branch (git push origin feature/your-feature)
7. Create a new Pull Request

Development Setup

To set up the package for development:

1. Clone the repository:

git clone https://github.com/diego-bernal/SequentialMeasurements.jl.git
cd SequentialMeasurements.jl

2. Start Julia and enter package mode by pressing ], then:

pkg> activate .
pkg> instantiate

3. Run the tests:

pkg> test

Adding New Features

• Measurement Schemes: Add new measurement schemes by creating a subtype of MeasurementScheme and implementing process_measurement
• Noise Models: Add new noise models by implementing new spectral density functions
• Control Sequences: Extend the control capabilities by adding new control sequence generators

License

This project is licensed under the MIT License - see the LICENSE file for details.