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Preparation and detection | Single-Qubit Gates

Preparation and detection of of Yb+ ions in electrodynamic traps [top]

A desired number of Yb+ ions is routinely trapped, laser cooled, and internal ionic quantum states are deterministically prepared [QIS18]. An image-intensified CCD camera allows for spatially resolved detection of resonance fluorescence originating from individual ions. Exemplary electrodynamic traps are depicted below. Figure 1a) shows images of the sequential loading of one, two, three, ..., 10 172Yb+ ions into a 3-dimensional microstructured linear Paul trap [QIS32]. Figure 1b) shows a 2-dimensional electrode structure that includes elements for trapping ions and magnetic field generating elements for ion manipulation and images of trapped Yb+ ions.

Figure 1a:
Upper panel: A microstructured linear Paul trap (based on a design by and realized in collaboration with Ferdinand Schmidt-Kaler and Kilian Singer, and STREP Microtrap). The trap integrates 70 independently controllable dc-electrodes and a magnetic field gradient.
Lower panel: Color-coded images of laser-induced resonance fluorescence close to 369 nm scattered by sequential loading of 172Yb+ ions into this trap.

Figure 1b:
Upper panel: A planar trap designed and build in our group. The trap consists of eleven dc electrode pairs (350 μm wide), six of which can carry currents to create a magnetic field gradient along the trap axis and three rf electrodes (about 150 μm each) lying between the electrode pairs (see inset).
Lower panel: Color-coded images of laser-induced resonance fluorescence close to 369 nm scattered by sequential loading of 172Yb+ ions into this trap.

Single-Qubit Gates [top]

One of the major obstacles when using quantum systems for information processing is the sensitivity of quantum superposition states to disturbances from their environment: any uncontrolled coupling to other systems may induce decoherence leading to an irreversible loss of quantum information. We have demonstrated essentially decoherence free arbitrary single qubit gates using 171Yb+ ions where two hyperfine states of an ion serve as a qubit.

References: [QIS14], [QIS10], [QIS13]

Figure 2:
Excitation probability of state of a single Yb+ ion averaged over 85 preparation-detection cycles as a function of mw pulse length. The fitted data (solid line), gives a Rabi frequency of 2.9165 x 2π kHz. The sub-unity contrast is due to imperfect initial state preparation (which will be improved in future experiments). These Rabi oscillations do not display any decoherence over experimentally relevant time scales.

Figure 3:
Data from a Ramsey-type experiment where the ion undergoes free precession between two subsequent microwave π/2-pulses (detuning of 103.9 x 2 π Hz, averaged over 100 realizations.) This experimental signal, too, is essentially free of decoherence and the contrast of the Ramsey fringes is only limited by the finite preparation efficiency.[QIS13]