Implementation of a Quantum Addressable Router Using Superconducting Qubits

The implementation of a quantum router capable of performing both quantum signal routing and quantum addressing (a <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msup> <a:mrow> <a:mrow> <a:mi mathvariant="normal">Q</a:mi> </a:mrow> </a:mrow> <a:mn>2</a:mn> </a:msup> </a:math> -router) represents a key step toward building quantum networks and quantum random access memories. We realize a <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"> <d:msup> <d:mrow> <d:mrow> <d:mi mathvariant="normal">Q</d:mi> </d:mrow> </d:mrow> <d:mn>2</d:mn> </d:msup> </d:math> -router that uses fixed-frequency transmon qubits to implement a routing protocol based on two native controlled- <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mi>i</g:mi> </g:math> gates. These gates leverage a large <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:mi>Z</i:mi> <i:mi>Z</i:mi> </i:math> interaction to selectively route information according to a quantum address. We find an estimated average routing fidelity of <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:mn>95.3</k:mn> <k:mi mathvariant="normal">%</k:mi> </k:math> , with errors arising primarily from decoherence or state preparation and measurement. We present a comprehensive calibration and characterization of both the c- <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"> <n:mi>i</n:mi> </n:math> gates and the overall routing protocol through randomized benchmarking techniques and state tomography.