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<h2 class="hd hd-2 unit-title">Two-qubit amplitude damping code</h2>
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Two-qubit amplitude damping code
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Amplitude damping is an important process in real physical systems; it models spontaneous emission, inelastic scattering, thermalization of spins to the lattice, and many other microscopic processes where energy is exchanged between the system and environment. In this problem, we study a quantum code adapted for this error mechanism. </p>
<p>
Recall that the amplitude damping channel for a single qubit is described by [mathjaxinline]{\cal E}(\rho ) = \sum _ k E_ k \rho E_ k^\dagger[/mathjaxinline], where the operation elements are </p>
<table id="a0000000002" class="equation" width="100%" cellspacing="0" cellpadding="7" style="table-layout:auto">
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<td class="equation" style="width:80%; border:none">[mathjax]E_0 = \left[ \begin{array}{cc} {1} &amp; {0}\\ {0} &amp; \sqrt{1-g} \end{array} \right] ~ ~ ~ ~ ~ ~ ~ ~ E_1 = \left[ \begin{array}{cc} {0} &amp; {\sqrt{g}}\\ {0} &amp; {0} \end{array} \right] \, .[/mathjax]</td>
<td class="eqnnum" style="width:20%; border:none;text-align:right">(1.1)</td>
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<p>
You may think of [mathjaxinline]g[/mathjaxinline] as being [mathjaxinline]g = 1-e^{-t/T_1}[/mathjaxinline], where [mathjaxinline]t[/mathjaxinline] is time and [mathjaxinline]T_1[/mathjaxinline] is the amplitude damping time constant. </p>
<p>
Let [mathjaxinline]|0_ L\rangle = |01\rangle[/mathjaxinline] and [mathjaxinline]|1_ L\rangle = |10\rangle[/mathjaxinline] be a quantum code encoding one logical qubit using two physical qubits. Define [mathjaxinline]|\psi \rangle = a|0_ L\rangle + b |1_ L\rangle[/mathjaxinline]. Compute the output state </p>
<table id="a0000000003" class="equation" width="100%" cellspacing="0" cellpadding="7" style="table-layout:auto">
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<td class="equation" style="width:80%; border:none">[mathjax]\rho ' = {\cal E}(|\psi \rangle ) = \sum _{j,k=\{ 0,1\} } (E_ j \otimes E_ k)\, |\psi \rangle \langle \psi | \, (E_ j\otimes E_ k)^\dagger[/mathjax]</td>
<td class="eqnnum" style="width:20%; border:none;text-align:right">(1.2)</td>
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<p>
which results when each physical qubit is subject to amplitude damping. &#160;<br/></p>
<p>
Please enter your answer as a matrix, ie a list of lists, of this form <tt class="tt">[ [ 1,0,0,0 ], [0,1,0,0], [0,0,1,0], [0,0,0,1] ]</tt>. Assume that [mathjaxinline]a[/mathjaxinline] and [mathjaxinline]b[/mathjaxinline] are real-valued. Use <tt class="tt">^</tt> for exponents, and explicitly include the multiplication operator <tt class="tt">*</tt>. You may use standard functions like <tt class="tt">sqrt</tt>. Express the results in terms of [mathjaxinline]g[/mathjaxinline], [mathjaxinline]a[/mathjaxinline], and [mathjaxinline]b[/mathjaxinline]. </p>
<p>
<p style="display:inline">[mathjaxinline]\rho ' =[/mathjaxinline]</p>
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Two-qubit amplitude damping code II
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In class we saw that distance between states could be measured by the trace distance. An alternate is the <em>fidelity</em>, which is equal to 1 for two states that are equal and 0 for two orthogonal states. In this way, it generalizes the inner product to density matrices. More information (not needed to complete this problem) on fidelity can be found <a href="https://en.wikipedia.org/wiki/Fidelity_of_quantum_states" target="_blank">here</a>. </p>
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Compute the fidelity [mathjaxinline]F(|\psi \rangle ,\rho ') = \sqrt{\langle \psi |\rho '|\psi \rangle }[/mathjaxinline] of [mathjaxinline]\rho '[/mathjaxinline] with respect to [mathjaxinline]|\psi \rangle[/mathjaxinline]. Express the result as a function of [mathjaxinline]g[/mathjaxinline]. </p>
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<p style="display:inline">[mathjaxinline]F(|\psi \rangle ,\rho ') =[/mathjaxinline]</p>
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Two-qubit amplitude damping code III
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Suppose we project the output state into the space orthogonal to [mathjaxinline]|00\rangle[/mathjaxinline] (say by performing a measurement of [mathjaxinline]Z\otimes I + I \otimes Z[/mathjaxinline] to measure the total excitation number), and keep only the cases when we do not obtain [mathjaxinline]|00\rangle[/mathjaxinline]. What is the resulting state? </p>
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Enter your answer using &#8220;ket" notation, e.g. [mathjaxinline]|0\rangle[/mathjaxinline] is [mathjaxinline]{\tt |0&gt;}[/mathjaxinline]. </p>
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<p style="display:inline">state =</p>
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<h2 class="hd hd-2 unit-title">Fun with stabilizers I: Groups and generators</h2>
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Groups and generators
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<p>
Stabilizers are a powerful way to describe quantum states and transformations. In this problem we explore some basic properties of stabilizer sets, which arise from the fact that a stabilizer is an <a href="http://en.wikipedia.org/wiki/Abelian_group" target="_blank">Abelian group</a>. </p>
<p>
Recall that if an [mathjaxinline]n[/mathjaxinline]-qubit state [mathjaxinline]|\psi \rangle[/mathjaxinline] is stabilized by [mathjaxinline]{\cal S} = \langle g_1, g_2, \ldots , g_ n \rangle[/mathjaxinline], then [mathjaxinline]g|\psi \rangle = |\psi \rangle[/mathjaxinline] for all [mathjaxinline]g\in S[/mathjaxinline]. To verify that [mathjaxinline]{\cal S}[/mathjaxinline] is an abelian group, we can observe that: </p>
<ul class="itemize">
<li>
<p>
[mathjaxinline]I^{\otimes n}[/mathjaxinline] is the identity element </p>
</li>
<li>
<p>
[mathjaxinline]g[/mathjaxinline] has an inverse: [mathjaxinline]gg^\dagger = I^{\otimes n}[/mathjaxinline] (up to factors of [mathjaxinline]\pm 1[/mathjaxinline] and [mathjaxinline]\pm i[/mathjaxinline], [mathjaxinline]g^\dagger = g[/mathjaxinline]) </p>
</li>
<li>
<p>
Multiplication of stabilizer elements is commutative and associative </p>
</li>
<li>
<p>
The set is closed under multiplication </p>
</li>
</ul>
<p>
In fact, [mathjaxinline]{\cal S}[/mathjaxinline] is a subgroup of the Pauli group, distinguished by an important fact: all elements of the stabilizer must commute with each other. It is because of this that all of the elements may share simultaneous eigenvectors. </p>
<p>
You are given that [mathjaxinline]{\cal S} = \{ {\tt XXIZ}, {\tt YXIY}, {\tt IZIX}, {\tt ZZII}, {\tt -YYIZ}, {\tt XYIY}, {\tt ZIIX}, {\tt IIII}\}[/mathjaxinline]. Give a minimal list of elements of [mathjaxinline]{\cal S}[/mathjaxinline] which can be combined by multiplication to produce all of the elements in [mathjaxinline]{\cal S}[/mathjaxinline]. We say that such a list is a set of <em>generators</em> of [mathjaxinline]{\cal S}[/mathjaxinline]: </p>
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Groups and generators II
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You are given that [mathjaxinline]\{ {\tt XIX},{\tt ZIY}\}[/mathjaxinline] generate [mathjaxinline]{\cal S}[/mathjaxinline]. Give a list of additional operators which are also in [mathjaxinline]{\cal S}[/mathjaxinline]. Your input should be a list of operators, eg of the form <tt class="tt">[XXX,YYY]</tt>: </p>
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Groups and generators III
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If [mathjaxinline]{\cal S}[/mathjaxinline] acts on an [mathjaxinline]n[/mathjaxinline]-qubit space, and the minimal generator set for [mathjaxinline]{\cal S}[/mathjaxinline] has [mathjaxinline]d[/mathjaxinline] elements, then what is the dimension of the vector space which is stabilized by [mathjaxinline]{\cal S}[/mathjaxinline]? &#160;<br/>&#160;<br/>Give your answer in terms of [mathjaxinline]n[/mathjaxinline] and [mathjaxinline]d[/mathjaxinline]. If necessary, remember to use <tt class="tt">^</tt> to indicate exponentiation. </p>
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<h2 class="hd hd-2 unit-title">Fun with stabilizers II: Elementary stabilizers</h2>
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Elementary stabilizers
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<p>
Stabilizers are one of the most useful way to describe states and transformations in quantum information. In this problem we epxlore some descriptions of basic stabilizer states. </p>
<p>
Recall that if an [mathjaxinline]n[/mathjaxinline]-qubit state [mathjaxinline]|\psi \rangle[/mathjaxinline] is stabilized by [mathjaxinline]S = \langle g_1, g_2, \ldots , g_ n \rangle[/mathjaxinline], then [mathjaxinline]g|\psi \rangle = |\psi \rangle[/mathjaxinline] for all [mathjaxinline]g\in S[/mathjaxinline]. Note that [mathjaxinline]g_1, g_2, \ldots , g_ n[/mathjaxinline] are the <em>generators</em> of [mathjaxinline]S[/mathjaxinline]. </p>
<p>
Give stabilizer generator sets for the following states (normalizations suppressed). Enter each set as a list of stabilizers, eg <tt class="tt">[XI,IX]</tt>: </p>
<ul class="itemize">
<li>
<p>
<p style="display:inline">[mathjaxinline]|0\rangle +i|1\rangle ~[/mathjaxinline]: </p>
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<li>
<p>
<p style="display:inline">[mathjaxinline]|1\rangle ~[/mathjaxinline]: </p>
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<p>
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<span id="solution_s12-wk3-stab0_solution_2"/>
</div></p>
</li>
<li>
<p>
<p style="display:inline">[mathjaxinline]|00\rangle +|11\rangle ~[/mathjaxinline]: </p>
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<p>
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<span id="solution_s12-wk3-stab0_solution_3"/>
</div></p>
</li>
<li>
<p>
<p style="display:inline">[mathjaxinline]|00\rangle -|11\rangle ~[/mathjaxinline]: </p>
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</p>
<p>
<div class="solution-span">
<span id="solution_s12-wk3-stab0_solution_4"/>
</div></p>
</li>
<li>
<p>
<p style="display:inline">[mathjaxinline]|01\rangle +|10\rangle ~[/mathjaxinline]: </p>
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</div>
</div></div>
</p>
<p>
<div class="solution-span">
<span id="solution_s12-wk3-stab0_solution_5"/>
</div></p>
</li>
<li>
<p>
<p style="display:inline">[mathjaxinline]|01\rangle -|10\rangle ~[/mathjaxinline]: </p>
<div class="inline" tabindex="-1" aria-label="Question 6" role="group"><div id="inputtype_s12-wk3-stab0_7_1" class=" capa_inputtype inline textline">
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</div></div>
</p>
<p>
<div class="solution-span">
<span id="solution_s12-wk3-stab0_solution_6"/>
</div></p>
</li>
<li>
<p>
<p style="display:inline">[mathjaxinline]|000\rangle +|111\rangle ~[/mathjaxinline]: </p>
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Elementary stabilizers II
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<p>
Give stabilizer generator sets for the following <em>vector spaces</em>, specified by the basis sets given. Enter each stabilizer generator set as a list of stabilizers, eg <tt class="tt">[XI,IX]</tt>. </p>
<ul class="itemize">
<li>
<p>
<p style="display:inline">{[mathjaxinline]|001\rangle[/mathjaxinline], [mathjaxinline]|110\rangle[/mathjaxinline]}</p>
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<p style="display:inline">{[mathjaxinline]|00\rangle +|11\rangle[/mathjaxinline], [mathjaxinline]|01\rangle +|10\rangle[/mathjaxinline]}</p>
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<h2 class="hd hd-2 unit-title">Fun with stabilizers III: Four-qubit stabilizer state</h2>
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Four-qubit stabilizer state
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Consider the stabilizer generator set </p>
<table id="a0000000008" class="eqnarray" cellspacing="0" cellpadding="7" width="100%" style="table-layout:auto">
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<td style="width:40%; border:none">&#160;</td>
<td style="vertical-align:middle; text-align:right; border:none">
[mathjaxinline]\displaystyle g_1[/mathjaxinline]
</td>
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[mathjaxinline]\displaystyle =[/mathjaxinline]
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<td style="vertical-align:middle; text-align:left; border:none">
[mathjaxinline]\displaystyle {\tt IIZZ}[/mathjaxinline]
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<td style="width:40%; border:none">&#160;</td>
<td class="eqnnum" style="width:20%; border:none;text-align:right">(1.6)</td>
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<tr id="a0000000010">
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[mathjaxinline]\displaystyle g_2[/mathjaxinline]
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[mathjaxinline]\displaystyle =[/mathjaxinline]
</td>
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[mathjaxinline]\displaystyle {\tt ZZII}[/mathjaxinline]
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<td style="width:40%; border:none">&#160;</td>
<td class="eqnnum" style="width:20%; border:none;text-align:right">(1.7)</td>
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[mathjaxinline]\displaystyle g_3[/mathjaxinline]
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[mathjaxinline]\displaystyle =[/mathjaxinline]
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[mathjaxinline]\displaystyle {\tt XXXX} \, .[/mathjaxinline]
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<td style="width:40%; border:none">&#160;</td>
<td class="eqnnum" style="width:20%; border:none;text-align:right">(1.8)</td>
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<p>
Note that these stabilizers act on a Hilbert space of four qubits. </p>
<p>
What is the dimension of the space stabilized by [mathjaxinline]S=\langle g_1,g_2,g_3\rangle[/mathjaxinline]? </p>
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Four-qubit stabilizer state II
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Give two four-qubit states which are stabilized by [mathjaxinline]{\cal S}[/mathjaxinline]. Please input your answer using &#8220;ket" notation, eg <tt class="tt">(|0011&gt;+|0000&gt;)/sqrt(2)</tt>. The two states should be orthogonal to each other. They need not be properly normalized. </p>
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<h2 class="hd hd-2 unit-title">Fun with stabilizers IV: Action of quantum gates on stabilizer states</h2>
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Action of quantum gates on stabilizer states
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<p>
Suppose [mathjaxinline]|\psi \rangle[/mathjaxinline] is stabilized by [mathjaxinline]{\cal S}[/mathjaxinline], such that [mathjaxinline]g|\psi \rangle = |\psi \rangle[/mathjaxinline] for all [mathjaxinline]g\in {\cal S}[/mathjaxinline]. Then [mathjaxinline]|\phi \rangle = U|\psi \rangle[/mathjaxinline] is stabilized by [mathjaxinline]{\cal S}' = U{\cal S}U^\dagger = \{ UgU^\dagger | g\in {\cal S}\}[/mathjaxinline], since </p>
<table id="a0000000015" class="equation" width="100%" cellspacing="0" cellpadding="7" style="table-layout:auto">
<tr>
<td class="equation" style="width:80%; border:none">[mathjax]UgU^\dagger |\phi \rangle = UgU^\dagger U|\psi \rangle = U |\psi \rangle = |\phi \rangle \, .[/mathjax]</td>
<td class="eqnnum" style="width:20%; border:none;text-align:right">(1.11)</td>
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<p>
Thus, we may often gain deep appreciation into the operation of a quantum circuit [mathjaxinline]U[/mathjaxinline] by studying how it transforms stabilizer sets (by conjugation), rather than how it transforms general quantum states (by multiplication). This is analogous to the difference between the Heisenberg and Schr&#246;dinger pictures of quantum mechanics. </p>
<p>
Consider the vector space [mathjaxinline]V = \{ |01\rangle +|10\rangle ,|00\rangle +|11\rangle \}[/mathjaxinline] stabilized by the generator set [mathjaxinline]{\cal S} = \langle XX\rangle[/mathjaxinline]. Give the new stabilizer [mathjaxinline]{\cal S}'[/mathjaxinline] resulting from operating on this two-qubit vector space with the following unitary gates. If the result is <em>not</em> a stabilizer space, enter <tt class="tt">None</tt>. Otherwise, enter the stabilizer as a list of generators, eg <tt class="tt">[IX,XI]</tt>. </p>
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<p>
<p style="display:inline">[mathjaxinline]U = H^{\otimes 2} = H\otimes H[/mathjaxinline]:</p>
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<p style="display:inline">[mathjaxinline]U = S^{\otimes 2} = S\otimes S[/mathjaxinline]:</p>
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<p style="display:inline">[mathjaxinline]U = T^{\otimes 2} = T\otimes T[/mathjaxinline]:</p>
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<p style="display:inline">[mathjaxinline]U = Z^{\otimes 2} = Z\otimes Z[/mathjaxinline]:</p>
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<p style="display:inline">[mathjaxinline]U = {\rm cnot} = ((I+Z)\otimes I + (I-Z)\otimes X)/2[/mathjaxinline]:</p>
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Action of quantum gates on stabilizer states II
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Consider the vector space [mathjaxinline]V[/mathjaxinline] stabilized by [mathjaxinline]{\cal S} = \langle g_1,g_2,g_3\rangle[/mathjaxinline], where </p>
<table id="a0000000016" class="eqnarray" cellspacing="0" cellpadding="7" width="100%" style="table-layout:auto">
<tr id="a0000000017">
<td style="width:40%; border:none">&#160;</td>
<td style="vertical-align:middle; text-align:right; border:none">
[mathjaxinline]\displaystyle g_1[/mathjaxinline]
</td>
<td style="vertical-align:middle; text-align:center; border:none">
[mathjaxinline]\displaystyle =[/mathjaxinline]
</td>
<td style="vertical-align:middle; text-align:left; border:none">
[mathjaxinline]\displaystyle {\tt IIZZ}[/mathjaxinline]
</td>
<td style="width:40%; border:none">&#160;</td>
<td class="eqnnum" style="width:20%; border:none;text-align:right">(1.12)</td>
</tr>
<tr id="a0000000018">
<td style="width:40%; border:none">&#160;</td>
<td style="vertical-align:middle; text-align:right; border:none">
[mathjaxinline]\displaystyle g_2[/mathjaxinline]
</td>
<td style="vertical-align:middle; text-align:center; border:none">
[mathjaxinline]\displaystyle =[/mathjaxinline]
</td>
<td style="vertical-align:middle; text-align:left; border:none">
[mathjaxinline]\displaystyle {\tt ZZII}[/mathjaxinline]
</td>
<td style="width:40%; border:none">&#160;</td>
<td class="eqnnum" style="width:20%; border:none;text-align:right">(1.13)</td>
</tr>
<tr id="a0000000019">
<td style="width:40%; border:none">&#160;</td>
<td style="vertical-align:middle; text-align:right; border:none">
[mathjaxinline]\displaystyle g_3[/mathjaxinline]
</td>
<td style="vertical-align:middle; text-align:center; border:none">
[mathjaxinline]\displaystyle =[/mathjaxinline]
</td>
<td style="vertical-align:middle; text-align:left; border:none">
[mathjaxinline]\displaystyle {\tt XXXX} \, .[/mathjaxinline]
</td>
<td style="width:40%; border:none">&#160;</td>
<td class="eqnnum" style="width:20%; border:none;text-align:right">(1.14)</td>
</tr>
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<p>
Give the new stabilizer [mathjaxinline]{\cal S}'[/mathjaxinline] resulting from operating on this four qubit vector space with the following unitary gates. If the result is <em>not</em> a stabilizer space, enter <tt class="tt">None</tt>. Otherwise, enter the stabilizer as a list of generators, eg <tt class="tt">[IX,XI]</tt>. </p>
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<p style="display:inline">[mathjaxinline]U_1 = H^{\otimes 4}[/mathjaxinline]:</p>
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<p style="display:inline">[mathjaxinline]U_2 = S^{\otimes 4}[/mathjaxinline]:</p>
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<p style="display:inline">[mathjaxinline]U_3 = Z^{\otimes 4} = Z\otimes Z \otimes Z \otimes Z[/mathjaxinline]:</p>
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Action of quantum gates on stabilizer states III
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Two stabilizer sets [mathjaxinline]{\cal S}[/mathjaxinline] and [mathjaxinline]{\cal S}'[/mathjaxinline] are equal if they contain the same stabilizer elements, ie if their generators generate the same sets. </p>
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For the above definitions of [mathjaxinline]U_1[/mathjaxinline], [mathjaxinline]U_2[/mathjaxinline], and [mathjaxinline]U_3[/mathjaxinline] and [mathjaxinline]{\cal S} = \langle g_1,g_2,g_3\rangle[/mathjaxinline], consider the statements below and check the adjoining box if the statement is true: </p>
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<p style="display:inline">[mathjaxinline]U_1 {\cal S} U_1^\dagger = {\cal S}[/mathjaxinline]: True?&#160;</p>
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<p style="display:inline">[mathjaxinline]U_2 {\cal S} U_2^\dagger = {\cal S}[/mathjaxinline]: True?&#160;</p>
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<p style="display:inline">[mathjaxinline]U_3 {\cal S} U_3^\dagger = {\cal S}[/mathjaxinline]: True?&#160;</p>
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<h2 class="hd hd-2 unit-title">Fun with stabilizers V: Stabilizer description of quantum circuit transformations</h2>
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Stabilizer description of quantum circuit transformations
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<p>
Consider the following simple quantum circuit: </p>
<p>
<center>
<img src="/assets/courseware/v1/7b4bf266c4621c3b33a8acefa278c7dd/asset-v1:MITx+8.371.1x+2T2018+type@asset+block/images_bell-circuit-stab-v2.png" width="300"/>
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<p>
The input state is [mathjaxinline]|00\rangle[/mathjaxinline], which is stabilized by [mathjaxinline]{\cal S}_0 = \langle {\tt IZ},{\tt ZI}\rangle[/mathjaxinline]. Give the stabilizers describing the state after the Hadamard and after the controlled-NOT gate. </p>
<p>
Work this out by using the fact that [mathjaxinline]U[/mathjaxinline] acting on a state stabilized by [mathjaxinline]{\cal S}[/mathjaxinline] produces a state stabilized by [mathjaxinline]U{\cal S}U^\dagger[/mathjaxinline]. </p>
<p>
You can also double-check yourself by working out the explicit quantum states produced in the circuit, and figuring out the stabilizers for each of the states. However, for circuits composed of <em>Clifford group</em> gates, namely circuits generated by [mathjaxinline]H[/mathjaxinline], [mathjaxinline]S[/mathjaxinline], and the controlled-NOT gate, it is much faster to work directly with the stabilizer. </p>
<p>
Enter each stabilizer as a list of generators, eg <tt class="tt">[IX,XI]</tt>: </p>
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<p>
<p style="display:inline">[mathjaxinline]{\cal S_1} = ~[/mathjaxinline]: </p>
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<h2 class="hd hd-2 unit-title">Topological QEC - A Projective Plane Code</h2>
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Topological QEC - A Projective Plane Code
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<p>
Quantum error correction codes can be constructed using graphs on topological surfaces, where vertices and edges correspond to certain stabilizer operations, and the distance of the code is given by the shortest non-trivial topological chain of errors. In this problem, we explore a specific instance of such a construction, on a <a href="http://en.wikipedia.org/wiki/Projective_plane" target="_blank">projective plane</a>. </p>
<p>
The projective plane in two dimensions, [mathjaxinline]\Re P^2[/mathjaxinline], can be drawn as a disc in which antipodal points on the boundary are identified. Recall that a cellulation [mathjaxinline]{\cal C}[/mathjaxinline] of a surface defines sets [mathjaxinline]F[/mathjaxinline], [mathjaxinline]E[/mathjaxinline], and [mathjaxinline]V[/mathjaxinline] of faces, edges, and vertices. For each [mathjaxinline]e\in E[/mathjaxinline], there corresponds a qubit on which [mathjaxinline]X_ e[/mathjaxinline] and [mathjaxinline]Z_ e[/mathjaxinline] are the Pauli [mathjaxinline]X[/mathjaxinline] and [mathjaxinline]Z[/mathjaxinline] operators. Let [mathjaxinline]E_ f \subset E[/mathjaxinline] be the set of edges around face [mathjaxinline]f\in F[/mathjaxinline], and let [mathjaxinline]E_ v \subset E[/mathjaxinline] be the set of edges attached to vertex [mathjaxinline]v\in V[/mathjaxinline]. For the set of all [mathjaxinline]f[/mathjaxinline] and [mathjaxinline]v[/mathjaxinline], we define </p>
<table id="a0000000020" class="equation" width="100%" cellspacing="0" cellpadding="7" style="table-layout:auto">
<tr>
<td class="equation" style="width:80%; border:none">[mathjax]A_ f = \bigotimes _{e\in E_ f} Z_ e[/mathjax]</td>
<td class="eqnnum" style="width:20%; border:none;text-align:right">(1.15)</td>
</tr>
</table>
<p>
and </p>
<table id="a0000000021" class="equation" width="100%" cellspacing="0" cellpadding="7" style="table-layout:auto">
<tr>
<td class="equation" style="width:80%; border:none">[mathjax]B_ v = \bigotimes _{e\in E_ v} X_ e \, .[/mathjax]</td>
<td class="eqnnum" style="width:20%; border:none;text-align:right">(1.16)</td>
</tr>
</table>
<p>
The set of all [mathjaxinline]A_ f[/mathjaxinline] and [mathjaxinline]B_ v[/mathjaxinline] is the stabilizer for the code. </p>
<p>
Give a list of stabilizers (three [mathjaxinline]A_ f[/mathjaxinline] and the single unique [mathjaxinline]B_ v[/mathjaxinline]) for the cellulation: </p>
<p>
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</center>
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<p>
This code acts on four qubits ([mathjaxinline]|E|=4[/mathjaxinline]), corresponding to the four edges, labeled [mathjaxinline]1[/mathjaxinline] through [mathjaxinline]4[/mathjaxinline]. Note there are only three distinct faces, labeled [mathjaxinline]A[/mathjaxinline], [mathjaxinline]B[/mathjaxinline], and [mathjaxinline]C[/mathjaxinline]. Be sure to verify that the stabilizers you give commute with each other. </p>
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Topological QEC - A Projective Plane Code II
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What state(s) do they stabilize? </p>
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You may input your answer using &#8220;ket" notation, eg <tt class="tt">(|0011&gt;+|0000&gt;)/sqrt(2)</tt>. Input boxes for two possible states are provided; enter <tt class="tt">None</tt> if the state is not needed. If you enter more than one state, make sure they are orthogonal to each other. States need not be normalized. </p>
<p>
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</div></div>
</p>
<p>
<div class="solution-span">
<span id="solution_s12-wk3-ppcode1-2_solution_1"/>
</div></p>
</div>
<div class="action">
<input type="hidden" name="problem_id" value="Topological QEC - A Projective Plane Code II" />
<div class="submit-attempt-container">
<button type="button" class="submit btn-brand" data-submitting="Submitting" data-value="Submit" data-should-enable-submit-button="True" aria-describedby="submission_feedback_s12-wk3-ppcode1-2" >
<span class="submit-label">Submit</span>
</button>
<div class="submission-feedback" id="submission_feedback_s12-wk3-ppcode1-2">
<span class="sr">Some problems have options such as save, reset, hints, or show answer. These options follow the Submit button.</span>
</div>
</div>
<div class="problem-action-buttons-wrapper">
<span class="problem-action-button-wrapper">
<button type="button" class="save problem-action-btn btn-default btn-small" data-value="Save">
<span class="icon fa fa-floppy-o" aria-hidden="true"></span>
<span aria-hidden="true">Save</span>
<span class="sr">Save your answer</span>
</button>
</span>
</div>
</div>
<div class="notification warning notification-gentle-alert
is-hidden"
tabindex="-1">
<span class="icon fa fa-exclamation-circle" aria-hidden="true"></span>
<span class="notification-message" aria-describedby="s12-wk3-ppcode1-2-problem-title">
</span>
<div class="notification-btn-wrapper">
<button type="button" class="btn btn-default btn-small notification-btn review-btn sr">Review</button>
</div>
</div>
<div class="notification warning notification-save
is-hidden"
tabindex="-1">
<span class="icon fa fa-save" aria-hidden="true"></span>
<span class="notification-message" aria-describedby="s12-wk3-ppcode1-2-problem-title">None
</span>
<div class="notification-btn-wrapper">
<button type="button" class="btn btn-default btn-small notification-btn review-btn sr">Review</button>
</div>
</div>
<div class="notification general notification-show-answer
is-hidden"
tabindex="-1">
<span class="icon fa fa-info-circle" aria-hidden="true"></span>
<span class="notification-message" aria-describedby="s12-wk3-ppcode1-2-problem-title">Answers are displayed within the problem
</span>
<div class="notification-btn-wrapper">
<button type="button" class="btn btn-default btn-small notification-btn review-btn sr">Review</button>
</div>
</div>
</div>
"
data-graded="True">
<p class="loading-spinner">
<i class="fa fa-spinner fa-pulse fa-2x fa-fw"></i>
<span class="sr">Loading…</span>
</p>
</div>
</div>
</div>
<div class="vert vert-2" data-id="block-v1:MITx+8.371.1x+2T2018+type@html+block@site_search_box011142">
<div class="xblock xblock-public_view xblock-public_view-html xmodule_display xmodule_HtmlBlock" data-has-score="False" data-usage-id="block-v1:MITx+8.371.1x+2T2018+type@html+block@site_search_box011142" data-runtime-version="1" data-block-type="html" data-course-id="course-v1:MITx+8.371.1x+2T2018" data-request-token="8dce2890abb511f180ff12541d743da1" data-init="XBlockToXModuleShim" data-runtime-class="LmsRuntime" data-graded="True">
<script type="json/xblock-args" class="xblock-json-init-args">
{"xmodule-type": "HTMLModule"}
</script>
<span><a href="/asset-v1:MITx+8.371.1x+2T2018+type@asset+block/NONE" id="dummy_course_static_link" style="display:none"/><a href="/courses/course-v1:MITx+8.371.1x+2T2018/jump_to_id/NONE" id="dummy_jump_link" style="display:none"/><script type="text/javascript">
var add_site_search = function(){
course_static_url = $('#dummy_course_static_link').attr('href').replace('/NONE', '');
jump_to_url = $('#dummy_jump_link').attr('href').replace('/NONE', '');
if (typeof String.prototype.startsWith != 'function') {
// see below for better implementation!
String.prototype.startsWith = function (str){
return this.indexOf(str) === 0;
};
}
if(typeof(String.prototype.trim) === "undefined")
{
String.prototype.trim = function()
{
return String(this).replace(/^\s+|\s+$/g, '');
};
}
var lb = String.fromCharCode(60);
var rb = String.fromCharCode(62);
var amp = String.fromCharCode(38);
var rlb = rb + lb;
var mke = function(x){ return lb + x + rb; }
var search_module_url = "";
var get_search_module_ficus = function(){
var cid = $('div.xblock').data('course-id');
if (cid){
console.log("cid = ", cid);
// search_module_url = "/courses/course-v1:MITx+8.371.1x+2T2018/" + cid + "/courseware/welcome/Search_this_course/";
search_module_url = "/courses/course-v1:MITx+8.371.1x+2T2018/courseware/welcome/Search_this_course/"; // automatically rewritten
console.log("3. search_module_url = ", search_module_url);
return;
}
var course_root_link = $('span.nav-item-course').find('a').attr('href');
if (course_root_link){
console.log("course_root_link = ", course_root_link);
search_module_url = course_root_link.replace("course/", "courseware/welcome/Search_this_course/");
console.log("2. search_module_url = ", search_module_url);
return
}
console.log("cannot determine search module url");
}
var get_search_module = function(){
// find search this module link
if (!($('div.course-index').length)){
return get_search_module_ficus();
}
$('div.course-index').find('nav').find('a').each(function(){
if ($(this).text().trim().startsWith("Search this course")){
search_module_url = $(this).attr('href');
console.log("search_module_url = ", search_module_url);
}
});
}
var go_to_search = function(){
get_search_module();
var sterm = $('#site-search-box').val();
// new_url = jump_to_url + "/Search_this_module/?q=" + sterm;
new_url = search_module_url + "?q=" + sterm;
console.log("sterm = ", sterm, " ; going to ", new_url);
window.location.href = new_url;
}
if (!$('#site-search-box').length){
$("nav.courseware").find("ol").append(lb + "section style='float:right'" + rlb + "input size='20'"
+ " id='site-search-box'"
+ rlb + "img src='" + course_static_url
+ "/images_search_glass.png'/" + rlb + "/input" + rlb + "/section" + rb);
}
$("#site-search-box").keypress(function(event) {
if (event.which == 13) {
event.preventDefault();
go_to_search();
}
});
// $('#site-search-box').bind("enterKey", go_to_search);
var get = function(x){
return eval(x);
}
return {'course_static_url': course_static_url,
'jump_to_url': jump_to_url,
'go_to_search': go_to_search,
'get_search_module': get_search_module,
'get_search_module_ficus': get_search_module_ficus,
'get': get,
}
}
var the_site_search = add_site_search();
var add_fix_transcript = function(){
if ($('div.wrap-instructor-info').length==0){
return;
}
$('div.xblock-student_view-video').each(function(key, vblock_e){
var vblock = $(vblock_e);
var vuid = vblock.data('usage-id').split('@');
var vid;
if (vuid.length==1){
vuid = vblock.data('usage-id').split(';_')
vid = vuid[5];
}else{
vid = vuid[2];
}
var mfnpre = vid.split("_video",1)[0];
var mfnid = mfnpre; // no periods
mfnpre = mfnpre.replace('8_370', '8.370'); // periods in gh filename
var lb = String.fromCharCode(60);
var rb = String.fromCharCode(62);
var mke = function(x){ return lb + x + rb; }
var ftid = "fix_transcript_" + mfnid;
if (!$('#' + ftid).length){
var html = lb + "span id='" + ftid + "' style='float:right'" + rb + lb + "a href='#'" + rb;
html += "contribute transcript fix" + mke("/a") + mke("/span");
console.log("html = ", html);
vblock.after(html)
}
$('#' + ftid).click(function(){
var cst = $('ol.subtitles').find('li.current');
var cindex = Number(cst.data('index'));
var gurl;
if (mfnpre.endsWith('_cq_sol')){
gurl = "https://github.com/mitocw/content-mit-8370x-cq-sol-subtitles/blob/master/";
}else{
gurl = "https://github.com/mitocw/content-mit-8370x-subtitles/blob/master/";
}
gurl += mfnpre + ".txt#L" + String(cindex + 10 + 1);
console.log("going to ", gurl);
window.open(gurl, "MITx 8.370x subtitle source");
});
});
}
try{
add_fix_transcript();
}
catch(err){
console.log(err);
}
try{
var rb = String.fromCharCode(62);
setTimeout(function(){ $('.math' + rb + 'span').css("border-left-color","transparent"); }, 3000);
setTimeout(function(){ $('.math' + rb + 'span').css("border-left-color","transparent"); }, 8000);
}
catch(err){
console.log(err);
}
</script></span>
</div>
</div>
</div>
</div>
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