Struct VirtualDistillation 

pub struct VirtualDistillation { /* private fields */ }

Virtual distillation mitigation based on the moment ratio Tr(O rho^M) / Tr(rho^M). Based on: [1] W. J. Huggins et al., “Virtual Distillation for Quantum Error Mitigation,” Phys. Rev. X, vol. 11, no. 4, p. 041036, Nov. 2021, doi: 10.1103/PhysRevX.11.041036.

Example

use cqlib_core::circuit::{Circuit, Qubit};
use cqlib_core::error_mitigation::VirtualDistillation;

let q0 = Qubit::new(0);
let mut circuit = Circuit::new(1);
circuit.x(q0).unwrap();

let _vd = VirtualDistillation::new(circuit, 2).unwrap();

Implementations

impl VirtualDistillation

pub fn new( circuit: Circuit, copies: usize, ) -> Result<Self, ErrorMitigationError>

Creates a new virtual distillation helper.

pub fn copies(&self) -> usize

Returns the configured number of copies.

pub fn set_copies(&mut self, copies: usize) -> Result<(), ErrorMitigationError>

Updates the configured number of copies.

pub fn build_copy_swap_circuit(&self) -> Result<Circuit, CircuitError>

Builds the virtual distillation circuit from the configured base circuit.

The returned circuit contains:

• copies disjoint copies of the base circuit preparation,
• one ancillary qubit (the last qubit, index copies * base_width), prepared in |+> by a Hadamard gate,
• a derangement of the copies implemented as a ladder of swap gates between adjacent copies, each controlled by the ancillary qubit (CSWAP).

This is the Hadamard-test circuit of the virtual distillation protocol: measuring X on the ancillary qubit (together with an observable on the first copy) yields Tr(O rho^M) / Tr(rho^M). Applying uncontrolled swaps instead would leave the permutation-symmetric state rho^M invariant and measure nothing related to the distilled moments.

pub fn run_denominator_circuit( &self, shots: usize, estimator: &Estimator<'_>, ) -> Result<(f64, f64), ErrorMitigationError>

Runs the denominator circuit and returns the estimated mean and variance.

• shots: the number of shots to run the circuit.
• estimator: an estimator that evaluates the virtual distillation circuit with the denominator observable (X on the ancillary qubit, identities elsewhere) and the provided shot count.

Returns

• (mu, var): the estimated mean and variance of Tr(rho^M).

pub fn run_numerator_circuit( &self, hamiltonian: &Hamiltonian, shots: usize, estimator: &Estimator<'_>, ) -> Result<(f64, f64), ErrorMitigationError>

Runs the numerator circuit and returns the estimated mean and variance.

• hamiltonian: the Hamiltonian to estimate on the virtual distillation circuit. It is expanded to the full circuit width with X on the ancillary qubit (see Self::expand_hamiltonian).
• shots: the number of shots to run the circuit.
• estimator: an estimator that evaluates the virtual distillation circuit, the given expanded Hamiltonian, and the provided shot count.

Returns

• (mu, var): the estimated mean and variance of Tr(H rho^M).

pub fn run_vd( &self, hamiltonian: &Hamiltonian, shots_numerator: usize, shots_denominator: usize, estimator: &Estimator<'_>, ) -> Result<(f64, f64), ErrorMitigationError>

Runs the virtual distillation circuit and returns the mean and variance.

• hamiltonian: a qis::Hamiltonian describing the observable to estimate for the original circuit.
• shots_numerator: the number of shots to run the numerator circuit.
• shots_denominator: the number of shots to run the denominator circuit.
• estimator: an estimator that evaluates circuits and returns (mu, var).

Returns

• mu_vd: the mitigated result of the observable on the original circuit.
• var_vd: the variance of the mitigated result.

Trait Implementations

impl Clone for VirtualDistillation

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for VirtualDistillation

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.