Hardware-Economic Manipulation of Dual-Type ${}^{171}$Yb$^+$ Qubits

Abstract

The dual-type qubit scheme is an emerging method to suppress crosstalk errors in scalable trapped-ion quantum computation and quantum network. Here we report a hardware-economic way to control dual-type $^{171}\mathrm{Yb}^+$ qubits using a single $355\,$nm mode-locked pulsed laser. Utilizing its broad frequency comb structure, we drive the Raman transitions of both qubit types encoded in the $S_{1/2}$ and the $F_{7/2}$ hyperfine levels, and probe their carrier transitions and the motional sidebands. We further demonstrate a direct entangling gate between the two qubit types. Our work can simplify the manipulation of the $^{171}\mathrm{Yb}^+$ qubits both at the hardware and the software level.

Figures (5)

• Figure 1: Experimental scheme. (a) Counter-propagating $355\,$nm pulsed laser beams with a repetition rate $\omega_r=2\pi\times 80\,$MHz control both the $S$-type and the $F$-type qubits, whose Raman transitions are bridged by the $k_S=158$ and the $k_F=45$ teeth of the frequency-comb structure, respectively. The laser beams from one direction are locked to the transition frequencies of the two qubit types by phase-locked loops (PLLs) to compensate the drift of $\omega_r$. The laser beams in the other direction are tuned by an arbitrary waveform generator (AWG) to select the carrier transitions or the blue and the red motional sidebands. (b) Relevant energy levels of $^{171}\mathrm{Yb}^+$. We use $411\,$nm and $3432\,$nm lasers to connect the $S$-type qubit spanned by $|0\rangle$ and $|1\rangle$, and the $F$-type qubit spanned by $|0^\prime\rangle$ and $|1^\prime\rangle$. We use $355\,$nm laser to drive Raman transitions of both qubit types, mediated by the upper energy levels. (c) Experimental sequence. The upper panel shows the initialization of an $S$-$F$ ion pair. The lower panel shows the detection of the $F$-type qubit (left) and the simultaneous detection of $S$-type and $F$-type qubits (right). The detection sequences are followed by fluorescence collection under global $370\,$nm laser beams which are not shown in the plot.
• Figure 2: Individual manipulation of $S$-type and $F$-type qubits. (a) Success probability of one attempt to prepare the $S$-$F$ ion pair. (b) and (c) Carrier Rabi oscillations of the $S$-type and the $F$-type qubits under the same intensity of the $355\,$nm laser. (d) Carrier and motional sideband spectra of the $F$-type qubit after sympathetic sideband cooling on the $S$-type qubit.
• Figure 3: Direct entanglement of an $S$-$F$ qubit pair. (a) The blue (bright) and red (dark) bars indicate the phase modulation sequence alternatingly applied on the $S$-type and $F$-type qubits, respectively. (b) Theoretical phase space trajectories of the two collective phonon modes when the qubits are in $|+ +^\prime\rangle$. (c) Population and (d) parity oscillation of the prepared Bell state of the $S$-$F$ pair.
• Figure 4: (a) Schematic of the laser setup. (b) Electronic system of the phase-locked loops for the $S$-type (upper) and the $F$-type (lower) qubits.
• Figure 5: Positions of two ions before and after the second ionization.