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A silicon quantum-dot-coupled nuclear spin qubit
摘要： Single nuclear spins in the solid state are a potential future platform for quantum computing, because they possess long coherence times and offer excellent controllability. Measurements can be performed via localized electrons, such as those in single atom dopants or crystal defects. However, establishing long-range interactions between multiple dopants or defects is challenging. Conversely, in lithographically defined quantum dots, tunable interdot electron tunnelling allows direct coupling of electron spin-based qubits in neighbouring dots. Moreover, the compatibility with semiconductor fabrication techniques may allow for scaling to large numbers of qubits in the future. Unfortunately, hyperfine interactions are typically too weak to address single nuclei. Here we show that for electrons in silicon metal–oxide–semiconductor quantum dots the hyperfine interaction is sufficient to initialize, read out and control single 29Si nuclear spins. This approach combines the long coherence times of nuclear spins with the flexibility and scalability of quantum dot systems. We demonstrate high-fidelity projective readout and control of the nuclear spin qubit, as well as entanglement between the nuclear and electron spins. Crucially, we find that both the nuclear spin and electron spin retain their coherence while moving the electron between quantum dots. Hence we envision long-range nuclear–nuclear entanglement via electron shuttling. Our results establish nuclear spins in quantum dots as a powerful new resource for quantum processing.
关键词： entanglement,hyperfine interaction,nuclear spins,quantum dots,silicon,coherence times,quantum computing
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - The Role of Trap Symmetry in an Atom-Chip Interferometer above the Bose-Einstein Condensation Threshold
摘要： Cold atom interferometers have demonstrated excellent performance and hold great prospects for time, gravity, acceleration and rotation measurements. Trapped interferometers, for example using atom chips, can potentially enable portable applications of theses sensors. Atom chip interferometers have been successfully demonstrated using Bose-Einstein condensates but are subject to the effect of atom-atom interactions which cause phase decoherence. In this study, we proposed an atom chip interferometer using a gas just above the condensation threshold to reduce the interaction effects. This proposal is similar to white light interferometry in the sense that the difference between the optical paths of the two arms must be close to zero to observe fringes. In a trapped interferometer this condition is analogous to maximizing the degree of symmetry between the two trapping potentials. We demonstrated that if the two trapping potentials are harmonic with slightly different curvatures inhomogeneous dephasing arises. This leads to a typical contrast decay time. Here we use 87Rb in the two states |a>=|F=1,mF=-1> and |b>=|F=2,mF=2>. Both states are trapped by the same magnetic field created by an atom chip. As described by the Breit-Rabi formula, the energies of the two levels |a> and |b> have a slightly different magnetic field dependence. We can use this difference to fine tune the curvature difference between the two trapping potentials. We perform Ramsey sequences and record the fringes as a function of the Ramsey time for several temperatures and values of curvature difference. We find a good agreement with the above formula. Coherence times of order 1s have been observed. We will describe the experiment, the model used to extract the contrast decay time and the limitations of this model due to atom interactions. The results open the way for experimental demonstration of atom chip accelerometers and gyroscopes.
关键词： trap symmetry,Ramsey sequences,atom-chip interferometer,Bose-Einstein condensation,coherence times
更新于2025-09-11 14:15:04