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We investigate the energy spectra and optical absorption of a 3D quantum dot–double quantum ring structure of GaAs/Al0.3Ga0.7As with adjustable geometrical parameters. In the effective mass approximation, we perform 3D numerical computations using as height profile a superposition of three Gaussian functions. Independent variations of height and width of the dot and of the rings and also of the dot–rings distance determine particular responses, useful in practical applications. We consider that a suitable manipulation of the geometrical parameters of this type of quantum coupling offer a variety of responses and, more important, the possibility of a fine adjusting in energy spectra and in the opportunity of choosing definite absorption domains, properties required for the improvement of the performances of optoelectronic devices.

We report the first complete characterization of single-qubit and two-qubit gate fidelities in silicon-based spin qubits, including cross talk and error correlations between the two qubits. To do so, we use a combination of standard randomized benchmarking and a recently introduced method called character randomized benchmarking, which allows for more reliable estimates of the two-qubit fidelity in this system, here giving a 92% fidelity estimate for the controlled-Zgate. Interestingly, with character randomized benchmarking, the two-qubit gate fidelity can be obtained by studying the additional decay induced by interleaving the two-qubit gate in a reference sequence of single-qubit gates only. This work sets the stage for further improvements in all the relevant gate fidelities in silicon spin qubits beyond the error threshold for fault-tolerant quantum computation.

We present an approach to estimate the single-particle energies in double InAs/InP nanowire quantum dots by combining an atomistic tight-binding approach with machine learning. The method works particularly well with a neural network and transfer learning, where we can accurately recover ground state energies with root-mean-square deviation around 1 meV by using only a small training set and capitalizing on earlier, smaller-scale computations. The training set is only a fraction of the multidimensional search space of possible dot sizes and inter-dot spacings. Besides the cases presented in this work, we expect this technique will interest other researchers involved in solving the inverse computational problem of matching spectra to nanostructure morphological properties.

This work studies the generation of the orbital angular momentum (OAM) beam in the double quantum dot-metal nanoparticle (DQD-MNP) system under the application of the OAM beam. First, an analytical model is derived to attain the relations of probe and generated fields as a distance function in the DQD-MNP system under OAM applied field and spontaneously generated coherence (SGC) components. The calculation here is of material property; it differs from others by calculating energy states of the DQDs and the computation of the transition momenta between quantum dot (QD)-QD and QD-wetting layer (WL) transitions. The orthogonalized plane wave (OPW) calculates QD-WL transitions and their momenta. The momentum calculation is essential to specify the Rabi frequency of the input field. Such characteristics are not used in earlier models. The results show that SGC is vital in increasing the generated field. The signal field generated in the DQD-MNP system doubles that from the DQD system alone. So, the DQD-MNP system is preferred to the DQD system. The generated field in the DQD-MNP for the strong coupling DQD-MNP system is higher than that for the weak coupling. Increasing the distance separating the DQD-MNP reduces the generated field. Higher OAM number reduce the generated field at a long distance in the device. The model is then extended to study the effect of incoherent pumping ( ) and the relations are modified to cover this part. The results show that reduces the generated field. While the results that compare the weak and strong coupling appear for the first, others compare well to the literature.

Accurate and efficient preparation of quantum state is a core issue in building a quantum computer. In this paper, we investigate how to prepare a certain single- or two-qubit target state from arbitrary initial states in semiconductor double quantum dots with only a few discrete control pulses by leveraging the deep reinforcement learning. Our method is based on the training of the network over numerous preparing tasks. The results show that once the network is well trained, it works for any initial states in the continuous Hilbert space. Thus repeated training for new preparation tasks is avoided. Our scheme outperforms the traditional optimization approaches based on gradient with both the higher efficiency and the preparation quality in discrete control space. Moreover, we find that the control trajectories designed by our scheme are robust against stochastic fluctuations within certain thresholds, such as the charge and nuclear noises.

The germanium (Ge) hut wire system has strong spin-orbit coupling, a long coherence time due to a very large heavy-light hole splitting, and the advantage of site-controlled large-scale hut wire positioning. These properties make the Ge hut wire a promising candidate for the realization of strong coupling of spin to superconducting resonators and scalability for multiple qubit coupling. We have coupled a reflection line resonator to a hole double quantum dot (DQD) formed in Ge hut wire. The amplitude and phase responses of the microwave resonator revealed that the charge stability diagrams of the DQD are in good agreement with those obtained from transport measurements. The DQD interdot tunneling rate is shown to be tunable from 6.2 GHz to 8.5 GHz, which demonstrates the ability to adjust the frequency detuning between the qubit and the resonator. Furthermore, we achieved a hole-resonator coupling strength of up to 15 MHz, with a charge qubit decoherence rate of 0.28 GHz. Meanwhile the hole spin-resonator coupling rate was estimated to be 3 MHz. These results suggest that holes of a DQD in a Ge hut wire are dipole coupled to microwave photons, potentially enabling tunable hole spin-photon interactions in Ge with an inherent spin-orbit coupling.

We study theoretically the supercurrent and the superconducting diode effect (SDE) in a structure comprising parallel-coupled double quantum dots (DQDs) sandwiched between two superconductor leads in the presence of a magnetic flux. The influence of the Rashba spin–orbit interaction (RSOI), which induces a spin-dependent phase factor in the dot–superconductor coupling strength, is taken into account by adopting the nonequilibrium Green’s function technique. This RSOI-induced phase factor serves as a driving force for the supercurrent in addition to the usual superconducting phase difference, and it leads to the system’s left/right asymmetry. Correspondingly, the magnitude of the positive and negative critical currents become different from each other: the so-called SDE. Our results show that the period, magnitude, and direction of the supercurrents depend strongly on the RSOI-induced phase factor, dots’ energy levels, interdot coupling strengths, and the magnetic flux. In the absence of magnetic flux, the diode efficiency is negative and may approach −2, which indicates the perfect diode effect with only negative flowing supercurrent in the absence of a positive one. Interestingly enough, both the sign and magnitude of the diode efficiency can be efficiently adjusted with the help of magnetic flux, the dots’ energy levels and the interdot coupling strength and thus provide a controllable SDE by rich means, such as gate voltage or host materials of the system.

This work simulates the use of a double quantum dot-metal nanoparticle (DQD-MNP) structure as a heat source in the water–ice system. The work here characterizes material properties that distinguish it from other works, in which the calculation of quantum dot (QD) and wetting layer (WL) energy levels and the WL-QD and QD-QD transition momenta is performed using the orthogonalized plane-wave approximation. An analytical relations for the temperature produced are derived to model this structure. The results show that a high temperature is obtained from the DQD-MNP system under the applied light intensity. This temperature increases with increasing MNP radius. Strong DQD-MNP coupling gives high temperature. Different matrices: GaAs, ZnO, and , where the DQD-MNP system is grown, are examined. The highest temperature is obtained from the matrix of high dielectric constant and shows similarity to the DQD structure. In this case, ZnO is preferred. This work suggests the use of low laser fluence for nanosurgery, which is less than the smallest power used in other research by three orders of magnitude. This result is clinically vital. The width of the water shell covering the DQD-MNP system increases as the MNP radius increases.

We study theoretically the Josephson diode effect (JDE) when realized in a system composed of parallel-coupled double-quantum dots (DQDs) sandwiched between two semiconductor nanowires deposited on an s-wave superconductor surface. Due to the combined effects of proximity-induced superconductivity, strong Rashba spin–orbit interaction, and the Zeeman splitting inside the nanowires, a pair of Majorana bound states (MBSs) may possibly emerge at opposite ends of each nanowire. Different phase factors arising from the superconductor substrate can be generated in the coupling amplitudes between the DQDs and MBSs prepared at the left and right nanowires, and this will result in the Josephson current. We find that the critical Josephson currents in positive and negative directions are different from each other in amplitude within an oscillation period with respect to the magnetic flux penetrating through the system, a phenomenon known as the JDE. It arises from the quantum interference effect in this double-path device, and it can hardly occur in the system of one QD coupled to MBSs. Our results also show that the diode efficiency can reach up to 50%, but this depends on the overlap amplitude between the MBSs, as well as the energy levels of the DQDs adjustable by gate voltages. The present model is realizable within current nanofabrication technologies and may find practical use in the interdisciplinary field of Majorana and Josephson physics.

Pathbreaking advancements in the field of nanofabrication techniques have put qubit technology at the forefront of quantum computation. Thanks to Silicon (Si) with its unparalleled strong foundation in the existing classical computation, it is considered to be a promising candidate for the development of complementary metal-oxide semiconductor compatible quantum architecture. This review article vividly describes the underlying physics of the qubit operation in quantum dots. Further, the article gives an overview of the current state of the art technology and the remarkable progress made in the field of charge and spin qubits in Si and allied heterostructures in the last two decades. Emphasis has been given to address the challenges and the accomplishments made so far in the field of Si-based charge and spin qubit technology. The article also discusses the future prospects of qubit technology and the measures being adopted worldwide for the physical realization of envisioned quantum devices.