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PDF (double-sided) - Physics Department, UCSB - University of ...

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ally determine an optimal value for each parameter. The easiest way to implement<br />

this approach is by varying one parameter at a time while holding all other parameters<br />

fixed to find a local optimum along the resulting line through parameter<br />

space. This process can be iteratively repeated for all free parameters.<br />

The main benefit <strong>of</strong> this method <strong>of</strong> optimization is that it provides a rough<br />

intuitive understanding <strong>of</strong> the behavior <strong>of</strong> S which can be used to expose flaws<br />

in the experimental setup or potential loopholes. This method <strong>of</strong> optimization,<br />

if implemented correctly, is also fairly immune to wasting time in parts <strong>of</strong> the<br />

parameter space that are known to have no hope <strong>of</strong> yielding a good outcome.<br />

There also are three shortcomings to this method:<br />

• For one, this method becomes very hard to implement if different parameters<br />

influence the value <strong>of</strong> S in a correlated way. For example, a change in the<br />

bias pulses used to sweep the qubits on or <strong>of</strong>f resonance will cause a change<br />

in the Z-rotation associated with the pulse, which will in turn affect the<br />

optimal value for the phase <strong>of</strong> the Bell rotation pulses.<br />

• The duty cycle with which this method will be able to query the oracle is<br />

fairly low as each completed run is followed by a period <strong>of</strong> analysis, parameter<br />

adjustment, and preparation for the next run. Not only does this reduce<br />

the rate at which information is learned about S, but the irregular breaks in<br />

254

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