Inhaltszusammenfassung

In this work, the construction and operation of a scalable trapped-ion quantum logic processor is presented. Quantum information is stored in Zeeman sublevels |↑⟩ and |↓⟩ of Calcium-40 ions and operated by laser Raman interactions. Central part of the processor is a segmented micro-structured linear Paul trap, which is also referred to as quantum charge-coupled device (QCCD). Single ions are shuttled along the trap axis between memory zones and a processing zone, where single- and two-qubit ...In this work, the construction and operation of a scalable trapped-ion quantum logic processor is presented. Quantum information is stored in Zeeman sublevels |↑⟩ and |↓⟩ of Calcium-40 ions and operated by laser Raman interactions. Central part of the processor is a segmented micro-structured linear Paul trap, which is also referred to as quantum charge-coupled device (QCCD). Single ions are shuttled along the trap axis between memory zones and a processing zone, where single- and two-qubit logic gates are driven with lasers. Single-qubit gates are performed with a fidelity of 99.9949(2)% and we achieve a qubit state preparation and measurement rate of 99.923(3)%. For two-qubit entangling gates a fidelity of 99.5(1)% is accomplished. High fidelity entangling gates require the ions to be close to the motional ground state, which imposes stringent requirements on coherent excitation from shuttling operations and anomalous heating of the ion trap. We achieve a low heating rate of three motional quanta per second at a radial mode frequency of 2π x 4.6 MHz. We actively stabilize this mode frequency to better than 2π x 20 Hz. Three different shuttling operations suffice for QCCD operation - transport, rotation and separation of ion crystals. Since suppressing motional excitation along the axial shuttling direction is experimentally challenging, we use a radial mode, as a bus mode for the entangling gate. Ion transport is performed with a motional excitation of 0.028(2) phonons on this mode within 30 µs, two-ion separation with 0.03(1) phonons (80µs) and two-ion rotation with 0.02(1) phonons (42µs). The experimental building blocks are combined to implement a scalable quantum logic circuit. We generate a maximally entangled four-qubit Greenberger-Horne-Zeilinger state |ψ⟩ = (|0000⟩+|1111⟩)/√2, which is an important resource for measurement-based quantum computing and quantum error correction. The constituent entangled ions are spatially separated over a distance of 1.8mm and full quantum state tomography yields a state fidelity of 94.4(3)%. A dynamical decoupling technique is employed to maintain 69(5)% coherence at a storage time of 1.1 seconds. Aside from probing the QCCD approach to scalable quantum computing, we demonstrate gate operations with a planar ion crystal: ground state cooling of a zigzag mode in a planar ion crystal is performed. For the first time, we realize the application of a spin-dependent optical dipole force on this mode, which is an important step towards an analog quantum simulator in a two-dimensional geometry.» weiterlesen» einklappen

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DDC Sachgruppe:
Physik