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            <ol class="chapter"><li><a href="qcgpu.html"><strong aria-hidden="true">1.</strong> QCGPU</a></li><li><ol class="section"><li><a href="getting-started.html"><strong aria-hidden="true">1.1.</strong> Getting Started</a></li></ol></li><li><a href="user-guide/user-guide.html"><strong aria-hidden="true">2.</strong> User Guide</a></li><li><ol class="section"><li><a href="user-guide/registers.html" class="active"><strong aria-hidden="true">2.1.</strong> Quantum Registers</a></li><li><a href="user-guide/gates.html"><strong aria-hidden="true">2.2.</strong> Quantum Gates</a></li><li><a href="user-guide/operations.html"><strong aria-hidden="true">2.3.</strong> Quantum Operations</a></li><li><a href="user-guide/examples.html"><strong aria-hidden="true">2.4.</strong> Examples</a></li><li><a href="user-guide/decoherence.html"><strong aria-hidden="true">2.5.</strong> Decoherence</a></li></ol></li><li><a href="algorithms/algorithms.html"><strong aria-hidden="true">3.</strong> Algorithms</a></li><li><ol class="section"><li><a href="algorithms/bernstein-vazirani.html"><strong aria-hidden="true">3.1.</strong> Bernstein-Vazirani</a></li><li><a href="algorithms/deutsch-jozsa.html"><strong aria-hidden="true">3.2.</strong> Deutsch-Jozsa</a></li><li><a href="algorithms/grover.html"><strong aria-hidden="true">3.3.</strong> Grovers</a></li><li><a href="algorithms/shor.html"><strong aria-hidden="true">3.4.</strong> Shors</a></li><li><a href="algorithms/super-dense.html"><strong aria-hidden="true">3.5.</strong> Super Dense Coding</a></li></ol></li></ol>
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                        <a class="header" href="user-guide/registers.html#quantum-registers" id="quantum-registers"><h1>Quantum Registers</h1></a>
<p>All of the simulation is done through quantum registers. QCGPU provides a struct as a register, but that contains fields to do with the OpenCL buffers and related items, so the creation of registers should be done through the provided methods.</p>
<p>The library is optimized for complex superpositions, so the registers are all dense. This means that the number of qubits you can initialize is directly related to the capacity / available memory of the device.</p>
<p>The register struct is called <code>State</code> and is available through <code>qcgpu::State</code>.</p>
<p>To create a register, the easiest way to do it is with the <code>State::new</code> method.
It takes two parameters, the number of qubits and the device to use. The device is given as a usize, and corresponds to the OpenCL device which the register will be on.</p>
<p>The following example creates a register with 5 qubits on the 1st device.</p>
<pre><pre class="playpen"><code class="language-rust"># extern crate qcgpu;

use qcgpu::State;

# fn main() {
let mut register = State::new(5, 0);
# }
</code></pre></pre>
<p>Notice that the register is mutable. This allows the register to change. Also, the device is 0 indexed.</p>
<p>The implementation is equivilent to the description of a state vector \( \lvert \psi \rangle \) with</p>
<p>\[ \lvert \psi \rangle = \sum_{j = 0}^{2^n - 1} \alpha_j \lvert j \rangle \]</p>
<p>where \(n\) is the number of qubits, \(\alpha_j\) is the amplitude and the state is \(j\) runs over all \(2^n\) basis states.</p>
<p>There is one other way to initialize a state. Given a bitstring, a register can be initialized in that state using the <code>State::from_bit_string</code> method. For example, to initialize a register with the value <code>0100</code> the following is used:</p>
<pre><pre class="playpen"><code class="language-rust"># extern crate qcgpu;

use qcgpu::State;

# fn main() {
let mut register = State::from_bit_string(&quot;|0100&gt;&quot;, 0);
# }
</code></pre></pre>
<p>The second argument is the same as before. The register that is outputed from this method is equivilent to the state</p>
<p>\[ \lvert 0100 \rangle\]</p>

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