High-Fidelity Preservation of Quantum Information During Trapped-Ion Transport

A promising scheme for building scalable quantum simulators and computers is the synthesis of a scalable system using interconnected subsystems. A prerequisite for this approach is the ability to faithfully transfer quantum information between subsystems. With trapped atomic ions, this can be realized by transporting ions with quantum information encoded into their internal states. Here, we measure with high precision the fidelity of quantum information encoded into hyperfine states of a ${{}^{171}\mathrm{Yb}}^{+}$ ion during ion transport in a microstructured Paul trap. Ramsey spectroscopy of the ion’s internal state is interleaved with up to 4000 transport operations over a distance of $280\mu \mathrm{m}$ each taking $12.8\mu \mathrm{s}$. We obtain a state fidelity of $99.9994({}_{-7}^{+6})\%$ per ion transport.

Figure 1

Schematic of the experiment. (a) The voltages $\tilde{U}(t)$ at the multichannel arbitrary waveform generator (MAWG) take the filter characteristic $G(s)$ of the electronics into account to produce suitable voltages $U(t)$ that transport the ion along the $x$ axis $M$ times between positions $A$ and $B$. (b) The timing of the transport operations is such that the ion is located equally long at $A$ and $B$. The ion transfer is sandwiched by two $\pi /2$ pulses.

Figure 2

(a) Ramsey fringes for 1 (black) and 4000 (red) ion transport operations. The relative phase $\phi$ between the two $\pi /2$ pulses is varied while the time between the pulses is kept constant. The decay of the amplitude due to the additional transport operations is hardly noticeable. (b) Three examples for the probability distributions that were used for the likelihood analysis of the data. The probability density $\rho (p_b|\tilde{b},N)$ for $\tilde{b}$ bright events out of $N$ trials is shown on the horizontal axis as a function of the probability $p_b$ for a projection into the state $|1⟩$ on the vertical axis.

Figure 3

Likelihood of the internal state fidelity $\mathcal{F}$ during ion transport. The loss of internal state fidelity due to the transfer of the ion is apparent, but the case of no loss of coherence is also compatible within the 68% confidence interval (shaded). The log likelihood is calculated by the numerical convolution of the likelihoods ${\mathcal{L}}_M$.