In this study, we address challenges in designing quantum information processors based on electron spin qubits in electrostatically-defined quantum dots (QDs). Numerical calculations of charge stability diagrams are presented for a realistic double QD device geometry. These methods generaize to linear QD arrays, and are based on determining the effective parameters of a Hubbard model Hamiltonian that is then diagonalized to find the many-electron ground state energy. These calculations enable the identification of gate voltage ranges that maintain desired charge states during qubit manipulation, and also account for electrical cross-talk between QDs. As a result, the methods presented here promise to be a valuable tool for developing scalable spin qubit quantum processors
arXiv
Hamiltonian engineering with time-ordered evolution for unitary control of electron spins in semiconductor quantum dots
Bohdan Khromets, Zach D. Merino, and Jonathan Baugh
We present a unitary control pulse design method for a scalable quantum computer architecture based on electron spins in lateral quantum dots. We employ simultaneous control of spin interactions and derive the functional forms of spin Hamiltonian parameter pulses for a universal set of 1- and 2-qubit logic gates. This includes selective spin rotations with the weak local g-factor variations in the pres- ence of the global oscillating field, and a Control-Phase operation with the simul- taneous control of g-factors and exchange couplings. We outline how to generalize the control scheme to multiqubit gate operations and the case of constrained or im- perfect control of the Hamiltonian parameters.
2023
[POSTER] Simulated Control of Spin Qubits in MOSFET Quantum Dot Linear Arrays
We present a novel nonparametric adaptive partitioning and stitching (NAPS) algorithm to estimate a probability density function (PDF) of a single variable. Sampled data is partitioned into blocks using a branching tree algorithm that minimizes deviations from a uniform density within blocks of various sample sizes arranged in a staggered format. The block sizes are constructed to balance the load in parallel computing as the PDF for each block is independently estimated using the nonparametric maximum entropy method (NMEM) previously developed for automated high throughput analysis. Once all block PDFs are calculated, they are stitched together to provide a smooth estimate throughout the sample range. Each stitch is an averaging process over weight factors based on the estimated cumulative distribution function (CDF) and a complementary CDF that characterize how data from flanking blocks overlap. Benchmarks on synthetic data show that our PDF estimates are fast and accurate for sample sizes ranging from 29 to 227, across a diverse set of distributions that account for single and multi-modal distributions with heavy tails or singularities. We also generate estimates by replacing NMEM with kernel density estimation (KDE) within blocks. Our results indicate that NAPS(NMEM) is the best-performing method overall, while NAPS(KDE) improves estimates near boundaries compared to standard KDE.
Integrated Control Addressing Circuits for a Surface Code Quantum Computer in Silicon
Rubaya Absar, Zach D. Merino, Hazem Elgabra, and 3 more authors
In Proceedings of the 17th ACM International Symposium on Nanoscale Architectures, Dec 2023
Quantum computers require a coordinated operation on a large number of quantum bits (qubits), presenting considerable obstacles such as system integration on a large scale, individual qubits control with precision, and significant error correction overhead. Silicon (Si) quantum dot (QD) spin qubits paired with CMOS control circuits promise a scalable solution due to its potential for large-scale integration utilizing well-established semiconductor technologies. This paper proposes a control addressing scheme for QD spin qubits operating on a node network architecture. Compared to the typical 2-dimensional array architecture, this approach considerably lowers the area constraint for control signal routing. Scalable circuits are designed to route the control signals for local and global operations of a surface code quantum error correction through the modular design of tiered switches controlled by demultiplexers. The proposed method is a critical step toward implementing scalable solid-state quantum processors.
Appl. Phys. Lett.
Stable electroluminescence in ambipolar dopant-free lateral p–n junctions
Lin Tian, Francois Sfigakis, Arjun Shetty, and 11 more authors
Dopant-free lateral p–n junctions in the GaAs/AlGaAs material system have attracted interest due to their potential use in quantum optoelectronics (e.g., optical quantum computers or quantum repeaters) and ease of integration with other components, such as single electron pumps and spin qubits. A major obstacle to integration has been the unwanted charge accumulation at the p–n junction gap that suppresses light emission, either due to enhanced non-radiative recombination or due to inhibition of p–n current. Typically, samples must frequently be warmed to room temperature to dissipate this built-up charge and restore light emission in a subsequent cooldown. Here, we introduce a practical gate voltage protocol that clears this parasitic charge accumulation, in situ at low temperature, enabling the indefinite cryogenic operation of devices. This reset protocol enabled the optical characterization of stable, bright, dopant-free lateral p–n junctions with electroluminescence linewidths among the narrowest (\<1 meV; \<0.5 nm) reported in this type of device. It also enabled the unambiguous identification of the ground state of neutral free excitons (heavy and light holes) as well as charged excitons (trions). The free exciton emission energies for both photoluminescence and electroluminescence are found to be nearly identical (within 0.2 meV or 0.1 nm). The binding and dissociation energies for free and charged excitons are reported. A free exciton lifetime of 237 ps was measured by time-resolved electroluminescence, compared to 419 ps with time-resolved photoluminescence.
2021
[POSTER] Microwave resonators for global control of electron spin qubits
@article{farmer2019universal,title={Universal sample size invariant measures for uncertainty quantification in density estimation},author={Farmer, Jenny and Merino, Zach and Gray, Alexander and Jacobs, Donald},journal={Entropy},volume={21},number={11},pages={1120},year={2019},publisher={MDPI},}