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Register a new userSemiconductor-inspired design principles for superconducting quantum computing
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Superconducting circuits offer tremendous design flexibility in the quantum regime culminating most recently in the demonstration of few qubit systems supposedly approaching the threshold for fault-tolerant quantum information processing. Competition in the solid-state comes from semiconductor qubits, where nature has bestowed some very useful properties which can be utilized for spin qubit based quantum computing. Here we begin to explore how selective design principles deduced from spin-based systems could be used to advance superconducting qubit science. We take an initial step along this path proposing an encoded qubit approach realizable with state-of-the-art tunable Josephson junction qubits. Our results show that this design philosophy holds promise, enables microwave-free control, and offers a pathway to future qubit designs with new capabilities such as with higher fidelity or, perhaps, operation at higher temperature. The approach is also especially suited to qubits based on variable super-semi junctions.
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Recent improvements in materials growth and fabrication techniques may finally allow for superconducting semiconductors to realize their potential. Here we build on a recent proposal to construct superconducting devices such as wires, Josephson junctions, and qubits inside and out-of single crystal silicon or germanium. Using atomistic fabrication techniques such as STM hydrogen lithography, heavily-doped superconducting regions within a single crystal could be constructed. We describe the characteristic parameters of basic superconducting elements---a 1D wire and a tunneling Josephson junction---and estimate the values for boron-doped silicon. The epitaxial, single-crystal nature of these devices, along with the extreme flexibility in device design down to the single-atom scale, may enable lower-noise or new types of devices and physics. We consider applications for such super-silicon devices, showing that the state-of-the-art transmon qubit and the sought-after phase-slip qubit can both be realized. The latter qubit leverages the natural high kinetic inductance of these materials. Building on this, we explore how kinetic inductance based particle detectors (e.g., photon or phonon) could be realized with potential application in astronomy or nanomechanics. We discuss super-semi devices (such as in silicon, germanium, or diamond) which would not require atomistic fabrication approaches and could be realized today.
We investigate the frontier between classical and quantum plasmonics in highly doped semiconductor layers. The choice of a semiconductor platform instead of metals for our study permits an accurate description of the quantum nature of the electrons constituting the plasmonic response, which is a crucial requirement for quantum plasmonics. Our quantum model allows us to calculate the collective plasmonic resonances from the electronic states determined by an arbitrary one-dimensional potential. Our approach is corroborated with experimental spectra, realized on a single quantum well, in which higher order longitudinal plasmonic modes are present. We demonstrate that their energy depends on the plasma energy, as it is also the case for metals, but also on the size confinement of the constituent electrons. This work opens the way towards the applicability of quantum engineering techniques for semiconductor plasmonics.
A niobium titanite nitride-based superconducting nanodevice in which the Josephson critical current can be modulated by a gate voltage - a Cooper-pair transistor - has proven a remarkably long parity lifetime exceeding one minute at temperatures close to absolute zero.
Different approaches in quantifying environmentally-induced decoherence are considered. We identify a measure of decoherence, derived from the density matrix of the system of interest, that quantifies the environmentally induced error, i.e., deviation from the ideal isolated-system dynamics. This measure can be shown to have several useful features. Its behavior as a function of time has no dependence on the initial conditions, and is expected to be insensitive to the internal dynamical time scales of the system, thus only probing the decoherence-related time dependence. For a spin-boson model - a prototype of a qubit interacting with environment - we also demonstrate the property of additivity: in the regime of the onset of decoherence, the sum of the individual qubit error measures provides an estimate of the error for a several-qubit system, even if the qubits are entangled, as expected in quantum-computing applications. This makes it possible to estimate decoherence for several-qubits quantum computer gate designs for which explicit calculations are exceedingly difficult.
A spin qubit in semiconductor quantum dots holds promise for quantum information processing for scalability and long coherence time. An important semiconductor qubit system is a double quantum dot trapping two electrons or holes, whose spin states encode either a singlet-triplet qubit or two single-spin qubits coupled by exchange interaction. In this article, we report progress on spin dephasing of two exchange-coupled spins in a double quantum dot. We first discuss the schemes of two-qubit gates and qubit encodings in gate-defined quantum dots or donor atoms based on the exchange interaction. Then, we report the progress on spin dephasing of a singlet-triplet qubit or a two-qubit gate. The methods of suppressing spin dephasing are further discussed. The understanding of spin dephasing may provide insights into the realization of high-fidelity quantum gates for spin-based quantum computing.
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