Scalable semiconductor quantum technologies

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The classical transistor enabled the first technological revolution in computing. The ultimate limits on information processing, however, are determined by quantum mechanics rather than classical physics. A new paradigm of quantum information science has emerged in recent decades that promises a second technological revolution - the quantum age'. The ability to efficiently simulate complex physical systems that obey quantum mechanics, for example, will enable untold new advances in medicine, energy, chemistry, materials engineering and many other fields. The key to unlock these advances is translating theoretical quantum circuits into real world devices, particularly with architectures that allow scaling to arbitrary size. Quantum information, however, is extremely fragile due to the process of decoherence. It remains a challenge to show that decoherence can be overcome in real devices, either by applying the theoretical tools of quantum error correction, or by exploiting topologically protected modes to store quantum states. The proposed research program uses two promising experimental platforms to test both strategies. The first strategy, using quantum error correction, is explored using spin qubits objects defined by the quantum states of an electron's spin. A single electron is confined in a small region of space called a quantum dot, and its spin can be manipulated with electromagnetic fields. We choose silicon as the host material because spin qubits can have very long coherence times in silicon, and quantum dots can be formed using CMOS-compatible fabrication methods, lending a great potential for scalability. We propose a novel network architecture for implementing a quantum error correction scheme with a very high tolerance for errors, called a surface code. The second strategy, topologically protected qubits, is explored in superconductor-semiconductor hybrid devices designed to realize special states known as Majorana fermions or parafermions. We will exploit a unique and scalable material system, based on InSb quantum wells, to engineer first demonstrations of manipulation and readout of topological qubits. A third thrust is on carbon nanotube (CNT) nano-mechanical resonators and explores their potential for measuring forces at the atomic scale. This builds on our demonstrated ability to measure sub-nanometer changes in the CNT vibration amplitude on microsecond timescales. We will apply this to detect the spin states of individual magnetic molecules grafted onto the CNT, which could serve as a basis for a new scanning probe technology.