diff --git a/src/intro/main.tex b/src/intro/main.tex index bdcfc80..70c3971 100644 --- a/src/intro/main.tex +++ b/src/intro/main.tex @@ -39,7 +39,7 @@ Much like in classical error correction, in \ac{qec} information is protected by mapping it onto codewords in an expanded -Hilbert space, thereby introducing redundancy. Take for example, the +Hilbert space, thereby introducing redundancy. Take, for example, the two-qubit code \cite{roffe_quantum_2019}, where we map% % \begin{align*} @@ -59,7 +59,7 @@ To determine if an error occurred, we want to know whether a state belongs% \footnote{ It is possible for a state to not completely lie in either subspace. - In this case, we can interpret the state as being in + In this case, we can interpret it as being in $\mathcal{C}$ or $\mathcal{F}$ with a certain probability. } to $\mathcal{C}$ or $\mathcal{F}$. @@ -69,8 +69,8 @@ described using operators \cite[Section 1.5]{griffiths_introduction_1995}. Because of the way these operators are defined, their eigenvalues correspond to the possible outcomes of measuring that observable, and the corresponding -eigenstates are the states that yield those values as measurements \cite[Section -3.3]{griffiths_introduction_1995}. +eigenstates are the determinate states that yield those values as +measurements \cite[Section 3.3]{griffiths_introduction_1995}. In our case, we need an operator with two eigenvalues, and the corresponding eigenspaces should be $\mathcal{C}$ and $\mathcal{F}$ respectively. For the two-qubit code, $Z_1Z_2$ is such an operator:% @@ -95,7 +95,7 @@ logical state $\ket{\psi}_\text{L}$, we prepare an ancilla qubit with state $\ket{0}_\text{A}$ and we entangle it with $\ket{\psi}_\text{L}$ in such a way that determining that instead indicates the eigenvalue. More specifically, using a syndrome -extraction circuit as shown in fig. \ref{fig:syndrome extraction}, we +extraction circuit as shown in Figure \ref{fig:syndrome extraction}, we transform the state of the three-qubit system as% % @@ -114,8 +114,8 @@ transform the state of the three-qubit system as% If $E \ket{\psi}_\text{L} \in \mathcal{C}$, the second term will cancel and we will deterministically measure $\ket{0}_\text{A}$ for the ancilla qubit. Similarly, if $E \ket{\psi}_\text{L} \in -\mathcal{F}$ we will deterministically measure $\ket{1}_\text{A}$. -In general, the resulting state of the three-qubit system will be a +\mathcal{F}$, we will deterministically measure $\ket{1}_\text{A}$. +In general, however, the resulting state of the three-qubit system will be a superposition of the two cases. Note that the expressions $P_\mathcal{C}$ and $P_\mathcal{F}$ above essentially constitute projection operators onto $\mathcal{C}$ and