Demonstration of the trapped-ion quantum CCD computer architecture.

The trapped-ion quantum charge-coupled device (QCCD) proposal1,2 lays out a blueprint for a universal quantum computer that uses mobile ions as qubits. Analogous to a charge-coupled device (CCD) camera, which stores and processes imaging information as movable electrical charges in coupled pixels, a QCCD computer stores quantum information in the internal state of electrically charged ions that are transported between different processing zones using dynamic electric fields. The promise of the QCCD architecture is to maintain the low error rates demonstrated in small trapped-ion experiments3-5 by limiting the quantum interactions to multiple small ion crystals, then physically splitting and rearranging the constituent ions of these crystals into new crystals, where further interactions occur. This approach leverages transport timescales that are fast relative to the coherence times of the qubits, the insensitivity of the qubit states of the ion to the electric fields used for transport, and the low crosstalk afforded by spatially separated crystals. However, engineering a machine capable of executing these operations across multiple interaction zones with low error introduces many difficulties, which have slowed progress in scaling this architecture to larger qubit numbers. Here we use a cryogenic surface trap to integrate all necessary elements of the QCCD architecture-a scalable trap design, parallel interaction zones and fast ion transport-into a programmable trapped-ion quantum computer that has a system performance consistent with the low error rates achieved in the individual ion crystals. We apply this approach to realize a teleported CNOT gate using mid-circuit measurement6, negligible crosstalk error and a quantum volume7 of 26 = 64. These results demonstrate that the QCCD architecture provides a viable path towards high-performance quantum computers.

Eliminating Leakage Errors in Hyperfine Qubits.

Population leakage outside the qubit subspace presents a particularly harmful source of error that cannot be handled by standard error correction methods. Using a trapped ^{171}Yb^{+} ion, we demonstrate an optical pumping scheme to suppress leakage errors in atomic hyperfine qubits. The selection rules and narrow linewidth of a quadrupole transition are used to selectively pump population out of leakage states and back into the qubit subspace. Each pumping cycle reduces the leakage population by a factor of ∼3, allowing for an exponential suppression in the number of cycles. We use interleaved randomized benchmarking on the qubit subspace to show that this pumping procedure has negligible side effects on the qubit subspace, bounding the induced qubit memory error by ≤2.0(8)×10^{-5} per cycle, and qubit population decay to ≤1.4(3)×10^{-7} per cycle. These results clear a major obstacle for implementations of quantum error correction and error mitigation protocols.

Experimental Study of Optimal Measurements for Quantum State Tomography.

Quantum tomography is a critically important tool to evaluate quantum hardware, making it essential to develop optimized measurement strategies that are both accurate and efficient. We compare a variety of strategies using nearly pure test states. Those that are informationally complete for all states are found to be accurate and reliable even in the presence of errors in the measurements themselves, while those designed to be complete only for pure states are far more efficient but highly sensitive to such errors. Our results highlight the unavoidable trade-offs inherent in quantum tomography.

From cars to carts. Increasing safety belt usage in shopping carts.

A modified reversal/multiple-baseline design across three supermarkets was used to examine the effectiveness of behavioral interventions in increasing the frequency of safety belt usage in shopping carts. Following low baseline rates, safety belt usage increased significantly during a prompt-plus-personal-contact condition at Stores 1 and 2. Safety belt usage then decreased, but remained above baseline levels, in a prompt-alone condition at both stores. However, at Store 1, usage increased when the personal-contact procedure was reintroduced but reversed to lower levels in a second prompt-alone condition. Finally, social validity scales indicated that adult shoppers with children favored both safety belts on carts and the experimental procedures used in this study and said that they intended to use safety belts on carts in the future. Implications and directions for further research are briefly discussed.

An evaluation of the referral and rehabilitation process among the minority handicapped.

This study examines factors believed to be predictive of the referral and rehabilitation process in this country. Using the Fiscal Year 1978 data from the Rehabilitation Services Administration, the study examines two general hypotheses found in the literature: (1) that minority status is likely to be a key determinant in the referral and rehabilitation process, and (2) that selected socio-demographic factors along with social supports and disability condition are likely to reveal direct influences on the referral and rehabilitation process. Multiple regression was used for the analysis. The analysis of the study revealed that the independent variables, for the most part, had either a direct or indirect effect on the outcome of referral and rehabilitation. More specifically, the results suggest that bias exist in the referral and rehabilitation process.