arXiv subjects

Stefanie Tenberg

Publications and source records attributed to Stefanie Tenberg.

3 recordsLinked to original sources

arXiv2018

Robust electric dipole transition at microwave frequencies for nuclear spin qubits in silicon

The nuclear spin state of a phosphorus donor ($^{31}$P) in isotopically enriched silicon-28 is an excellent host to store quantum information in the solid state. The spin's insensitivity to electric fields yields a solid-state qubit with record coherence times, but also renders coupling to other quantum systems very challenging. Here, we describe how to generate a strong electric dipole ($>100$ Debye) at microwave frequencies for the nuclear spin. This is achieved by applying a magnetic drive to the spin of the donor-bound electron, while simultaneously controlling its charge state with electric fields. Under certain conditions, the microwave magnetic drive also renders the nuclear spin resonance frequency and electric dipole strongly insensitive to electrical noise, yielding long ($>1$ ms) dephasing times and robust gate operations. The nuclear spin could then be strongly coupled to microwave resonators, with a vacuum Rabi splitting of order 1 MHz, or to other nuclear spins, nearly half a micrometer apart, via strong electric dipole-dipole interaction. This work brings the $^{31}$P nuclear qubit into the realm of hybrid quantum systems and opens up new avenues in quantum information processing.

cond-mat.mes-hall↗

arXiv2017

Silicon quantum processor with robust long-distance qubit couplings

Practical quantum computers require the construction of a large network of highly coherent qubits, interconnected in a design robust against errors. Donor spins in silicon provide state-of-the-art coherence and quantum gate fidelities, in a physical platform adapted from industrial semiconductor processing. Here we present a scalable design for a silicon quantum processor that does not require precise donor placement and allows hundreds of nanometers inter-qubit distances, therefore facilitating fabrication using current technology. All qubit operations are performed via electrical means on the electron-nuclear spin states of a phosphorus donor. Single-qubit gates use low power electric drive at microwave frequencies, while fast two-qubit gates exploit electric dipole-dipole interactions. Microwave resonators allow for millimeter-distance entanglement and interfacing with photonic links. Sweet spots protect the qubits from charge noise up to second order, implying that all operations can be performed with error rates below quantum error correction thresholds, even without any active noise cancellation technique.

cond-mat.mes-hall↗

arXiv2015

Narrowing of the Overhauser field distribution by feedback-enhanced dynamic nuclear polarization

In many electron spin qubit systems coherent control is impaired by the fluctuating nuclear spin bath of the host material. Previous experiments have shown dynamic nuclear polarization with feedback to significantly prolong the inhomogeneous dephasing time $T_2^*$ by narrowing the distribution of nuclear Overhauser field fluctuations. We present a model relating the achievable narrowing of the Overhauser field to both the pump rate and the noise magnitude and find reasonable agreement with experimental data. It shows that former experiments on gated GaAs quantum dots were limited by the pump rate of the pumping mechanism used. Here we propose an alternative feedback scheme using electron dipole spin resonance. Sequentially applying two ac electric fields with frequencies slightly detuned from the desired Larmor frequency results in a pump curve with a stable fixed point. Our model predicts that $T_2^*$ values on the order of microseconds can be achieved.

cond-mat.mes-hall↗