<i>In situ</i> midcircuit qubit measurement and reset in a single-species trapped-ion quantum computing system

We implement midcircuit measurement and reset (MCMR) operations on a full-scale trapped-ion quantum computing system by using metastable qubit states in <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mmultiscripts> <a:mi>Yb</a:mi> <a:none/> <a:mo>+</a:mo> <a:mprescripts/> <a:none/> <a:mn>171</a:mn> </a:mmultiscripts> </a:math> ions. We compare two methods for isolating data qubits from measured qubits: one shelves the data qubits into the metastable state and the other drives the measured qubit to the metastable state without disturbing the other qubits. We experimentally demonstrate both methods on a crystal of two <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mmultiscripts> <b:mi>Yb</b:mi> <b:none/> <b:mo>+</b:mo> <b:mprescripts/> <b:none/> <b:mn>171</b:mn> </b:mmultiscripts> </b:math> ions using both the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:msub> <c:mi>S</c:mi> <c:mrow> <c:mn>1</c:mn> <c:mo>/</c:mo> <c:mn>2</c:mn> </c:mrow> </c:msub> </c:math> ground-state hyperfine clock qubit and the <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:msub> <d:mi>S</d:mi> <d:mrow> <d:mn>1</d:mn> <d:mo>/</d:mo> <d:mn>2</d:mn> </d:mrow> </d:msub> <d:mtext>−</d:mtext> <d:msub> <d:mi>D</d:mi> <d:mrow> <d:mn>3</d:mn> <d:mo>/</d:mo> <d:mn>2</d:mn> </d:mrow> </d:msub> </d:mrow> </d:math> optical qubit. These MCMR methods result in errors on the data qubit of about <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mrow> <e:mn>2</e:mn> <e:mo>%</e:mo> </e:mrow> </e:math> without degrading the measurement fidelity. With straightforward reductions in laser noise, these errors can be suppressed to less than <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:mrow> <f:mn>0.1</f:mn> <f:mo>%</f:mo> </f:mrow> </f:math> . The demonstrated methods allow MCMR to be performed in a single-species ion chain without shuttling or additional qubit-addressing optics, greatly simplifying the system architecture and allowing straightforward integration with existing trapped-ion quantum computers.