Abstract
There are two general requirements to harness the computational power of quantum mechanics: the ability to manipulate the evolution of an isolated system and the ability to faithfully extract information from it. Quantum error correction and simulation often make a more exacting demand: the ability to perform non-destructive measurements of specific correlations within that system. We realize such measurements by employing a protocol adapted from [S. Nigg and S. M. Girvin, Phys. Rev. Lett. 110, 243604 (2013)], enabling real-time selection of arbitrary register-wide Pauli operators. Our implementation consists of a simple circuit quantum electrodynamics (cQED) module of four highly-coherent 3D transmon qubits, collectively coupled to a high-Q superconducting microwave cavity. As a demonstration, we enact all seven nontrivial subset-parity measurements on our three-qubit register. For each we fully characterize the realized measurement by analyzing the detector (observable operators) via quantum detector tomography and by analyzing the quantum back-action via conditioned process tomography. No single quantity completely encapsulates the performance of a measurement, and standard figures of merit have not yet emerged. Accordingly, we consider several new fidelity measures for both the detector and the complete measurement process. We measure all of these quantities and report high fidelities, indicating that we are measuring the desired quantities precisely and that the measurements are highly non-demolition. We further show that both results are improved significantly by an additional error-heralding measurement. The analyses presented here form a useful basis for the future characterization and validation of quantum measurements, anticipating the demands of emerging quantum technologies.
Highlights
Building on impressive progress in control [1,2], measurement [3,4], and coherence [5,6], experimental quantum information science is addressing increasingly complex challenges, such as quantum error correction [7,8,9,10,11,12] and quantum simulation [13,14]
We use these interactions to engineer measurements of multiqubit properties via an ancilla qubit, adapting a proposal by Nigg and Girvin [26]. We demonstrate this protocol with a 3 þ 1 qubit system by performing all seven nontrivial three-qubit subset-parity measurements, Oi ⊗ Oj ⊗ Ok∶Ox ∈ fI; Zg, excluding III. This set is of particular interest: when combined with single-qubit rotations, it generates the measurements of all possible product operators, which include those needed for stabilizer-based quantum error correction [8]
III E, we present measurement process tomography: What makes the detector click and what happens to the state after measurement? And in Sec
Summary
Building on impressive progress in control [1,2], measurement [3,4], and coherence [5,6], experimental quantum information science is addressing increasingly complex challenges, such as quantum error correction [7,8,9,10,11,12] and quantum simulation [13,14]. Residual interactions are of particular concern as they lead to correlated and coherent errors, can scale badly as additional qubits are added, and are potentially catastrophic for quantum error correction [15,16,17] These challenges raise two questions: how do we design hardware and software to directly implement multiqubit measurements while addressing these concerns, and. We demonstrate this protocol with a 3 þ 1 qubit system by performing all seven nontrivial three-qubit subset-parity measurements, Oi ⊗ Oj ⊗ Ok∶Ox ∈ fI; Zg, excluding III This set is of particular interest: when combined with single-qubit rotations, it generates the measurements of all possible product operators, which include those needed for stabilizer-based quantum error correction [8]. This may prove to be a useful feature, as heraldedsuccess gates can be efficiently used for universal quantum computation [29,30,31]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
