diff --git a/docs/source/guide/lre-5-theory.md b/docs/source/guide/lre-5-theory.md index 0bf40c810..c87212920 100644 --- a/docs/source/guide/lre-5-theory.md +++ b/docs/source/guide/lre-5-theory.md @@ -33,7 +33,7 @@ LRE leverages the flexible configuration space of layerwise unitary folding, allowing for a more nuanced mitigation of errors by treating the noise level of each layer of the quantum circuit as an independent variable. -## Step 1: Intentionally create multiple noise-scaled but logically equivalent circuits +## Step 1: Create noise-scaled circuits The goal is to create noise-scaled circuits of different depths where the layers in each circuit are scaled in a specific pattern as a result of unitary folding. This pattern is often described by the vector of scale factor vectors @@ -44,7 +44,7 @@ Suppose we're interested in the value of some observable in an $n$-qubit circuit Each layer can have a different scale factor and we can create $M$ such variations of the scaled circuit. Let $\{λ_1, λ_2, λ_3, \ldots, λ_M\}$ be the scale factors vectors used to create multiple variations of the noise-scaled circuits $\{C_{λ_1}, C_{λ_2}, C_{λ_3}, \ldots, C_{λ_M}\}$ such that each vector $λ_i$ defines the scale factors for the different layers in the input circuit $\{{λ^1}_i, {λ^2}_i, {λ^3}_i, \ldots, {λ^l}_i\}^T$. -If $d$ is the chosen degree of our multivariate polynomial, $M_j(λ_i, d)$ corresponds to the terms in the polynomial arranged in increasing order. In general, the monomial terms for a variable $l$ up to degree $d$ can be determined through the [stars and bars method](https://en.wikipedia.org/wiki/Stars_and_bars_%28combinatorics%29). +If $d$ is the chosen degree of our multivariate polynomial, we define $M_j(λ_i, d)$ to be the terms in the polynomial arranged in increasing order. In general, the number of monomial terms with $l$ variables up to degree $d$ can be determined through the [stars and bars method](https://en.wikipedia.org/wiki/Stars_and_bars_%28combinatorics%29). $$ \text{total number of terms in the monomial basis with max degree } d = \binom{d + l}{d} @@ -72,7 +72,8 @@ Finding the coefficients in the linear combination becomes a problem solvable th ## Step 2: Extrapolate to the noiseless limit -Each noise scaled circuit $C_{λ_i}$ has an expectation value $\langle O(λ_i) \rangle$ associated with it such that we can define a vector of the noisy expectation values $z = (\langle O(λ_1) \rangle, \langle O(λ_2) \rangle, \ldots, \langle O(λ_M)\rangle)^T$. These have a coefficient of linear combination associated with them as shown below: +Each noise scaled circuit $C_{λ_i}$ has an expectation value $\langle O(λ_i) \rangle$ associated with it such that we can define a vector of the noisy expectation values $z = (\langle O(λ_1) \rangle, \langle O(λ_2) \rangle, \ldots, \langle O(λ_M)\rangle)^T$. +These values can then be combined via a linear combination to estimate the ideal value $variable$. $$ O_{\mathrm{LRE}} = \sum_{i=1}^{M} \eta_i \langle O(λ_i) \rangle.