noise_channel.h

Go to the documentation of this file.

/*
Copyright 2025 SQUANDER Contributors

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

#pragma once

#include "density_matrix.h"
#include <string>

namespace squander {
namespace density {

class NoiseChannel {
public:
  virtual ~NoiseChannel() = default;

  virtual void apply(DensityMatrix &rho) = 0;

  virtual std::string get_name() const = 0;
};

class DepolarizingChannel : public NoiseChannel {
public:
  DepolarizingChannel(int qbit_num, double error_rate);

  void apply(DensityMatrix &rho) override;
  std::string get_name() const override { return "Depolarizing"; }

  double get_error_rate() const { return error_rate_; }
  int get_qbit_num() const { return qbit_num_; }

private:
  int qbit_num_;
  double error_rate_;
};

class AmplitudeDampingChannel : public NoiseChannel {
public:
  AmplitudeDampingChannel(int target_qbit, double gamma);

  void apply(DensityMatrix &rho) override;
  std::string get_name() const override { return "AmplitudeDamping"; }

  double get_gamma() const { return gamma_; }
  int get_target_qbit() const { return target_qbit_; }

private:
  int target_qbit_;
  double gamma_; 
};

class PhaseDampingChannel : public NoiseChannel {
public:
  PhaseDampingChannel(int target_qbit, double lambda);

  void apply(DensityMatrix &rho) override;
  std::string get_name() const override { return "PhaseDamping"; }

  double get_lambda() const { return lambda_; }
  int get_target_qbit() const { return target_qbit_; }

private:
  int target_qbit_;
  double lambda_; 
};

} // namespace density
} // namespace squander