Benchmarking of dynamically corrected gates for the exchange-only spin qubit in 1/f1/f noise environment

We study theoretically the responses of the dynamically corrected gates to time-dependent noises in the exchange-only spin qubit system. We consider $1/f$ noises having spectra proportional to $1/\omega^\alpha$, where the exponent $\alpha$ indicates the strength of correlation within the noise. The quantum gate errors due to noises are extracted from a numerical simulation of Randomized Benchmarking, and are compared between the application of uncorrected operations and that of dynamically corrected gates robust against the hyperfine noise. We have found that for $\alpha\gtrsim1.5$, the dynamically corrected gates offer considerable reduction in the gate error and such reduction is approximately two orders of magnitude for the experimentally relevant noise exponent. On the other hand, no improvement of the gate fidelity is provided for $\alpha\lesssim1.5$. This critical value $\alpha_c\approx1.5$ is comparatively larger than that for the cases for the singlet-triplet qubits. The filter transfer functions corresponding to the dynamically corrected gates are also computed and compared to those derived from uncorrected pulses. Our results suggest that the dynamically corrected gates are useful measures to suppress the hyperfine noise when operating the exchange-only qubits.Comment: 10 pages,6 figure

Leakage and sweet spots in triple-quantum-dot spin qubits: A molecular-orbital study

A triple-quantum-dot system can be operated as either an exchange-only qubit or a resonant-exchange qubit. While it is generally believed that the decisive advantage of the resonant-exchange qubit is the suppression of charge noise because it is operated at a sweet spot, we show that the leakage is also an important factor. Through molecular-orbital-theoretic calculations, we show that when the system is operated in the exchange-only scheme, the leakage to states with double electron occupancy in quantum dots is severe when rotations around the axis 120$^\circ$ from $\hat{z}$ is performed. While this leakage can be reduced by either shrinking the dots or separating them further, the exchange interactions are also suppressed at the same time, making the gate operations unfavorably slow. When the system is operated as a resonant-exchange qubit, the leakage is 3-5 orders of magnitude smaller. We have also calculated the optimal detuning point which minimizes the leakage for the resonant-exchange qubit, and have found that although it does not coincide with the double-sweet-spot for the charge noise, they are rather close. Our results suggest that the resonant-exchange qubit has another advantage that leakage can be greatly suppressed compared to the exchange-only qubit, and operating at the double-sweet-spot point should be optimal both for reducing charge noise and suppressing leakage.Comment: 11 pages, 14 figure

SELF-ADAPTED PLANNER FOR LANGUAGE MODEL BASED QUESTION ANSWERING EVALUATION

早稲田大学修士(工学)master thesi

Universal singlet-triplet qubits implemented near the transverse sweet spot

The key to realizing fault-tolerant quantum computation for singlet-triplet (ST) qubits in semiconductor double quantum dot (DQD) is to operate both the single- and two-qubit gates with high fidelity. The feasible way includes operating the qubit near the transverse sweet spot (TSS) to reduce the leading order of the noise, as well as adopting the proper pulse sequences which are immune to noise. The single-qubit gates can be achieved by introducing an AC drive on the detuning near the TSS. The large dipole moment of the DQDs at the TSS has enabled strong coupling between the qubits and the cavity resonator, which leads to a two-qubit entangling gates. When operating in the proper region and applying modest pulse sequences, both single- and two-qubit gates are having fidelity higher than 99%. Our results suggest that taking advantage of the appropriate pulse sequences near the TSS can be effective to obtain high-fidelity ST qubits.Comment: 13 pages, 7 figure

Modeling the Obstacle Performance of Cable-Towed Vehicles

The forces required to pull wheeled vehicles over idealized terrain obstacles were studied. Scale models and computer simulations were used to evaluate the peak forces for single-axle vehicles equipped with rigid wheels and pneumatic tires. A scale model of a rimless spoke wheel was also tested. The results from the rigid wheel and pneumatic-tired simulations approximated those for the scale models. The rimless spoke wheel model required relatively high towing forces. The computer results indicated that towing forces could be reduced by a factor of three in some situations by using low pressure tires instead of rigid wheels. Even with low pressure tires, it is not possible to pull vehicles over obstacles larger than approximately 1 / 5 of the wheel diameter, if towing forces are not to exceed the vehicle weight