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valbert4 committed Dec 15, 2024
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2 changes: 1 addition & 1 deletion codes/classical/analog/lattice/points_into_lattices.yml
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The \textit{lattice quantizer problem} is to find a lattice whose \textit{fundamental Voronoi cell} \(\Pi\), the Voronoi cell at the origin, has the smallest possible normalized second moment,
\begin{align}
G(\Pi)=\frac{\frac{1}{n}\int_{\Pi}x\cdot x\,dx}{\text{Vol}(\Pi)^{1+2/n}}\,.
G(\Pi)=\frac{\frac{1}{n}\int_{\Pi}x\cdot x\,\textnormal{d}x}{\text{Vol}(\Pi)^{1+2/n}}\,.
\end{align}
Higher-dimensional lattices yield quantizers with lower normalized second moments than the 1D integer lattice \cite{manual:{P. L. Zador, Development and evaluation of procedures for quantiZing multivariate distributions, Ph.D. Dissertation, Stanford Univ., 1963},doi:10.1109/TIT.1982.1056490}.
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As such, a design can be used to determine the average of degree-\(\leq t\) polynomials \(p\) over \(X\),
\begin{align}
\int_{X}dxp(x)={\textstyle \frac{1}{|D|}}\sum_{x\in D}p(x)~,
\int_{X}\textnormal{d}xp(x)={\textstyle \frac{1}{|D|}}\sum_{x\in D}p(x)~,
\end{align}
where the integral is over \(X\) (given some measure \(d x\)), while the sum is over the design \(D\subset X\).
A \textit{weighted design} is a design for which each term \(p(x)\) in the above sum must be multiplied by a weight \(w(x)\) in order to be equal to the left-hand side.
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2 changes: 1 addition & 1 deletion codes/quantum/groups/rotors/stabilizer/css/zero_pi.yml
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An alternative codeword basis in terms of angular position states is
\begin{align}
\begin{split}
|\overline{+}\rangle&=\intop_{U(1)}d\phi\left|\phi,\phi\right\rangle \\|\overline{-}\rangle&=\intop_{U(1)}d\phi\left|\phi,\phi+\pi\right\rangle~.
|\overline{+}\rangle&=\intop_{U(1)}\textnormal{d}\phi\left|\phi,\phi\right\rangle \\|\overline{-}\rangle&=\intop_{U(1)}\textnormal{d}\phi\left|\phi,\phi+\pi\right\rangle~.
\end{split}
\end{align}
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2 changes: 1 addition & 1 deletion codes/quantum/oscillators/tiger/tiger.yml
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Using multi-index notation, a projected coherent state can be written in two ways,
\begin{align}
|\boldsymbol{\alpha}\rangle_{\boldsymbol{\Delta}}^{H}&\propto\int d\boldsymbol{\phi}e^{i\boldsymbol{\phi}(H\hat{\mathbf{n}}-\boldsymbol{\Delta})}|\boldsymbol{\alpha}\rangle\\&\propto\sum_{H\mathbf{n}=\boldsymbol{\Delta}}\frac{\boldsymbol{\alpha}^{\mathbf{n}}}{\sqrt{\mathbf{n}!}}|\mathbf{n}\rangle~,
|\boldsymbol{\alpha}\rangle_{\boldsymbol{\Delta}}^{H}&\propto\int \textnormal{d}\boldsymbol{\phi}e^{i\boldsymbol{\phi}(H\hat{\mathbf{n}}-\boldsymbol{\Delta})}|\boldsymbol{\alpha}\rangle\\&\propto\sum_{H\mathbf{n}=\boldsymbol{\Delta}}\frac{\boldsymbol{\alpha}^{\mathbf{n}}}{\sqrt{\mathbf{n}!}}|\mathbf{n}\rangle~,
\end{align}
where \(\boldsymbol{\alpha}\) is a complex vector, \(\boldsymbol{\Delta}\) is an integer vector, and \(\boldsymbol{\phi}\) is a vector of phases iterating over the elements of the group generated by \(H\).
Tiger codewords are of the above form, and their phase-space values \(\boldsymbol{\alpha}\) lie on a torus embedded in the complex sphere of fixed-energy coherent coherent states, satisfying \(|\alpha_j|^2 = 1\).
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2 changes: 1 addition & 1 deletion codes/quantum/oscillators/uncategorized/penrose.yml
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Letting \(|T\rangle\) be a Penrose tiling, the codeword corresponding to this tiling is a superposition of all points in the tiling's orbit under all Euclidean transformations,
\begin{align}
|\overline{T}\rangle=\int dg|gT\rangle~,
|\overline{T}\rangle=\int \textnormal{d}g|gT\rangle~,
\end{align}
where \(g\) is a Euclidean transformation.
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2 changes: 1 addition & 1 deletion codes/quantum/properties/block/quantum_perfect.yml
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protection: |
Perfect codes have been classified.
For qubits (\(q=2\)), the only nontrivial codes are the stabilizer code family \([[(4^r-1)/3, (4^r-1)/3 - 2r, 3]]\) for \(r \geq 2\), obtained from Hamming codes over \(GF(4)\) via the Hermitian construction \cite{arxiv:quant-ph/9607027,arxiv:quant-ph/9608006}.
For qudits, the corresponding family is the \([[\frac{q^{2r}-1}{q^{2}-1},q^{n-2r},3]]\) family of quantum twisted codes \cite{arxiv:0907.0049,doi:10.1002/(SICI)1520-6610(2000)8:3<174::AID-JCD3>3.0.CO;2-T}.
For qudits, the corresponding family is the \([[\frac{q^{2r}-1}{q^{2}-1},q^{n-2r},3]]_q\) family of quantum twisted codes \cite{arxiv:0907.0049,doi:10.1002/(SICI)1520-6610(2000)8:3<174::AID-JCD3>3.0.CO;2-T}.
# The trivial code (\(k=n\)) is also perfect.

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2 changes: 1 addition & 1 deletion codes/quantum/qubits/nonstabilizer/self_complementary.yml
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detail: 'Self-complementary quantum codes consisting of computational basis states whose bitstrings are sufficiently spaced apart correct at least one \hyperref[topic:ad]{AD} error \cite[Thm. 2.5]{arxiv:0712.2586}\cite[Thm. 2]{arxiv:0907.5149}.'
cousins:
- code_id: bits_into_bits
detail: 'A binary code is called \textit{self-complementary} if, for each codeword \(c\), its negation \(\overline{c}\) is also a codeword.'
detail: 'A binary code is called \textit{self-complementary} if, for each codeword \(c\), its negation \(\overline{c}\) is also a codeword. Any self-complementary \((n,K,d > 1)\) classical code yields an \(((n,K/2,2))\) self-complementary quantum code whose quantum codewords are superpositions of the classical codewords and their complements \cite[Lemma 1]{arxiv:quant-ph/0701065}.'


# Begin Entry Meta Information
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2 changes: 1 addition & 1 deletion codes/quantum/qubits/qubits_into_qubits.yml
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- 'The decoder determining the most likely error given a noise channel is called the \textit{maximum probability error} (MPE) decoder. For few-qubit codes (\(n\) is small), MPE decoding can be based by creating a lookup table. For infinite code families, the size of such a table scales exponentially with \(n\), so approximate decoding algorithms scaling polynomially with \(n\) have to be used.'
- '\begin{defterm}{Effective distance and hook errors}
\label{topic:effective-distance}
Decoders are characterized by an effective distance (a.k.a. \textit{circuit-level distance}), the minimum number of faulty operations during syndrome measurement that is required to make an undetectable error. A code is \textit{distance-preserving} if it admits a decoder whose circuit-level distance is equal to the code distance. A particularly dangerous class of syndrome measurement circuit faults are \textit{hook errors}, which are faults that cause more than one data-qubit error \cite{arxiv:quant-ph/0110143}. Hook errors occur at specific places in a syndrome extraction circuit and can sometimes be removed by re-ordering the gates of the circuit. If not, the use of \textit{flag qubits} (see \cite{preset:GottesmanBook}) to detect hook errors may be necessary to yield fault-tolerant decoders.
Decoders are characterized by an effective distance (a.k.a. \textit{circuit-level distance}), the minimum number of faulty operations during syndrome measurement that is required to make an undetectable error. A code is \textit{distance-preserving} if it admits a decoder whose circuit-level distance is equal to the code distance. A particularly dangerous class of syndrome measurement circuit faults are \textit{hook errors}, which are ancilla faults that cause more than one data-qubit error \cite{arxiv:quant-ph/0110143}. Hook errors occur at specific places in a syndrome extraction circuit and can sometimes be removed by re-ordering the gates of the circuit. If not, the use of \textit{flag qubits} (see \cite{preset:GottesmanBook}) to detect hook errors may be necessary to yield fault-tolerant decoders.
\end{defterm}'
fault_tolerance:
- 'There are lower bounds on the overhead of fault-tolerant QEC in terms of the capacity of the noise channel \cite{arxiv:2202.00119}. A more stringent bound applies to geometrically local QEC due to the fact that locality constrains the growth of the entanglement that is needed for protection \cite{arxiv:2302.04317}.'
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- code_id: stabilizer_over_gfqsq
cousins:
- code_id: quantum_perfect
detail: 'The \([[\frac{q^{2r}-1}{q^{2}-1},q^{n-2r},3]]\) family of quantum twisted codes are the only perfect Galois-qudit codes \cite{arxiv:0907.0049,doi:10.1002/(SICI)1520-6610(2000)8:3<174::AID-JCD3>3.0.CO;2-T}.'
detail: 'The \([[\frac{q^{2r}-1}{q^{2}-1},q^{n-2r},3]]_q\) family of quantum twisted codes are the only perfect Galois-qudit codes \cite{arxiv:0907.0049,doi:10.1002/(SICI)1520-6610(2000)8:3<174::AID-JCD3>3.0.CO;2-T}.'
- code_id: twisted_bch


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