RAISE-TAQS: Inverting the design paradigm: Tunable qubits in hybrid photonic materials as a scalable platform for quantum photonic devices

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The advent of solid state electronics altered human society through the emergence of small, portable, and powerful computers. Quantum technologies promise an equally revolutionary change in information transmission, information processing, and sensing. However, there is an enormous gap between the existing demonstration of few-bit devices and the highly integrated multi-bit devices required to realize these potential gains. New paradigms for the design of scalable, robust quantum devices are the key to realizing the potential of this field. One of the major challenges is that traditional electronic devices contain many instances of a small number of fundamental components (e.g. transistors). The tiny, but inevitable, variation between each component can be overcome by using components such as amplifiers and discriminators. However, components like amplifiers cannot be used in quantum devices. As a result, most simple quantum devices to date have engineered the entire device around the unique properties of the particular quantum bits that are available. This approach is not scalable. We propose to develop a new design strategy that will allow the individual quantum bits to be tuned after fabrication and during device operation. We believe this approach will not only overcome the scalability challenges, but will also enable a new form of quantum parallel processing that will speed up device operation. We will develop the materials and device architectures that allow the tuning while preserving the strong interactions between the quantum bits that are crucial for quantum device operation. We will also develop new algorithms that take advantage of this parallel processing opportunity. We will train students for the emerging field of quantum device engineering through a series of new courses and summer research programs.TechnicalWe propose to invert the design paradigm for quantum devices, creating a platform in which each qubit can be tuned into resonance with a device-level design wavelength. Our prototype qubit will be the orientation of a single hole spin confined in an InAs Quantum Dot Molecule (QDM): a closely spaced pair of QDs in which the emission / absorption wavelength tunes strongly with applied electric field. Conceptually, the proof-of-concept device we will develop is fairly simple: a photonic crystal cavity containing multiple qubits that can be individually tuned into resonance with the cavity mode in order to controllably implement quantum logic functions. To realize this concept, we will develop metal / dielectric metamaterials that can be grown within III-V epitaxial structures. We will develop and employ inverse design methods to create photonic cavities that leverage these new metamaterials to allow application of electric fields to individual qubits while retaining high cavity quality (Q) and small cavity mode volume (V). In parallel, we will design high fidelity gates that build toward single-shot three-qubit gates that enable faster computation and lower circuit depth. We will train students for the emerging field of quantum device engineering through: 1) A cohort undergraduate researcher exchange program; 2) Development of a new undergrad / grad course on photonic metamaterials; and 3) A two-week hands-on summer program for high school underrepresented minorities.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.