Wording
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@ -84,7 +84,7 @@ as a vector}
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The so called Bra-ket or Dirac notation is especially appropriate,
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The so called Bra-ket or Dirac notation is especially appropriate,
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having been proposed by Paul Dirac in 1939 for the express purpose
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having been proposed by Paul Dirac in 1939 for the express purpose
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of simplifying quantum mechanical notation \cite{dirac_new_1939}.
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of simplifying quantum mechanical notation \cite{dirac_new_1939}.
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Two new symbols are introduced, \emph{bra}s $\bra{\cdot}$ and
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Two new symbols are defined, \emph{bra}s $\bra{\cdot}$ and
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\emph{ket}s $\ket{\cdot}$.
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\emph{ket}s $\ket{\cdot}$.
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Kets denote ordinary vectors, while bras denote their Hermitian conjugates.
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Kets denote ordinary vectors, while bras denote their Hermitian conjugates.
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For example, two vectors specified by the labels $a$ and $b$
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For example, two vectors specified by the labels $a$ and $b$
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@ -119,7 +119,8 @@ Their inner product is $\braket{a\vert b}$.
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.%
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.%
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\end{align*}%
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\end{align*}%
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%
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%
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\ldots When not ambiguous in the context, the tensor product symbol may be omitted, e.g.
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\ldots When not ambiguous in the context, the tensor product
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symbol may be omitted, e.g.,
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\begin{align*}
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\begin{align*}
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\ket{0} \otimes \ket{0} = \ket{0}\ket{0}
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\ket{0} \otimes \ket{0} = \ket{0}\ket{0}
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.%
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.%
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@ -128,7 +129,7 @@ Their inner product is $\braket{a\vert b}$.
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As we will see, the core concept that gives quantum computing its
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As we will see, the core concept that gives quantum computing its
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power is entanglement. When two quantum mechanical systems are
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power is entanglement. When two quantum mechanical systems are
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entangled, measuring the state of one will collapse the state of the other.
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entangled, measuring the state of one will collapse that of the other.
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Take for example two subsystems with the overall state
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Take for example two subsystems with the overall state
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%
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%
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\begin{align*}
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\begin{align*}
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@ -137,9 +138,9 @@ Take for example two subsystems with the overall state
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.%
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.%
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\end{align*}
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\end{align*}
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%
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%
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If we measure the state of the first subsystem as $\ket{0}$, we can
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If we measure the first subsystem as being in $\ket{0}$, we can
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be certain that a measurement of the second subsystem will also yield $\ket{0}$.
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be certain that a measurement of the second subsystem will also yield $\ket{0}$.
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For brevity, we write the state of the combined system as%
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Introducing a new notation for entangled states, we can write%
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%
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%
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\begin{align*}
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\begin{align*}
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\ket{\psi} = \frac{1}{\sqrt{2}} \left( \ket{00} + \ket{11} \right)
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\ket{\psi} = \frac{1}{\sqrt{2}} \left( \ket{00} + \ket{11} \right)
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