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arXiv:1611.10016 · Journal of the Optical Society of America B

Optical barium ion qubit

Dahyun Yum, D. De Munshi, Tarun Dutta, Manas Mukherjee

Published Jul 17, 2017• 25 citations
arXivHTMLPDF

Abstract

We demonstrate an optical single qubit based on a narrow 6S1/2 to 5D5/2 quadrupole transition of a single Ba+ ion operated by only diode-based lasers. The characteristic properties of the qubit are discussed. We observe continuous bit-flip oscillations at a rate of about 250 kHz, which is fast enough for a qubit operation as compared to the measured coherence time of over 3 ms. We also present a technique, called randomized benchmarking, to quantify the bit-flip error in each qubit NOT gate operation.

DOI
10.1364/josab.34.001632

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Physical Review A•Feb 1, 1992•15 citations
We demonstrate an optical single qubit based on a narrow 6S1/2 to 5D5/2 quadrupole transition of a single Ba+ ion operated by only diode-based lasers. The characteristic properties of the qubit are discussed. We observe continuous bit-flip oscillations at a rate of about 250 kHz, which is fast enough for a qubit operation as compared to the measured coherence time of over 3 ms. We also present a technique, called randomized benchmarking, to quantify the bit-flip error in each qubit NOT gate operation.
Barium ions are trapped and Doppler cooled in a linear Paul trap with the goal of demonstrating state initialization, single-qubit operations and detection. Rabi rotations are demonstrated on the 6S1/2 ↔ 6P3/2 transition using single pulses from a mode-locked Ti:Sapphire laser, and some evidence for the same on the more useful 6S1/2] ↔ 6P1/2 transition is shown. With the goal of entangling the polarization mode of emitted photons with the spin state of the ion in the trap in mind, single photon generation and detection ability is demonstrated. A stabilized 1.762 µm laser is used on the 6S1/2 → 5D5/2 transition to demonstrate the ability to state selectively shelve the ion from the ground state to be used as readout. Using the techniques that will enable qubit operations and readout, several quantities of interest in 137Ba+ are measured either for the first time or to higher accuracy than previously achieved.
The electric dipole-forbidden, quadrupole $6{S}_{1/2}\ensuremath{\leftrightarrow}5{D}_{3/2}$ transition in Ba+{}^{+}+ near 2051 nm, with a natural linewidth of 13 mHz, is attractive for potential observation of parity nonconservation, and also as a clock transition for a barium ion optical frequency standard. This transition also offers a direct means of populating the metastable 5D3/25{D}_{3/2}5D3/2​ state to measure the nuclear magnetic octupole moment in the odd barium isotopes. Light from a diode-pumped, solid-state Tm,Ho:YLF laser operating at 2051 nm is used to coherently drive this transition between resolved Zeeman levels in a single trapped 138{}^{138}138Ba+{}^{+}+ ion. The frequency of the laser is stabilized to a high-finesse Fabry-P\'erot cavity at 1025 nm after being frequency doubled. Rabi oscillations on this transition indicate a laser-ion coherence time of 3 ms, most likely limited by ambient magnetic field fluctuations.
Ultracold ions provide one of the most promising platforms for quantum computing and make it possible to reach record coherence times, the fidelity of preparation and readout operations, and single- and two-qubit operations. Encoding quantum information in an optical qubit based on the 2S1/2(F=0,mF=0)^{2}{{S}_{{1/2}}}(F = 0,{{m}_{F}} = 0)2S1/2​(F=0,mF​=0) → 2D3/2(F=2,mF=0)^{2}{{D}_{{3/2}}}(F = 2,{{m}_{F}} = 0)2D3/2​(F=2,mF​=0) quadrupole transition in the 171Yb+ ion at a wavelength of 435.5 nm, which has potential advantages over similar systems in the scaling of the number of qubits and their sensitivity to fluctuations of the magnetic field, is proposed and experimentally studied. The proposed optical qubit in ytterbium is compared to other most widespread types of ion qubits. Experimental results on the implementation of the Pauli-X single-qubit operation are given. The fidelity of the operation is 96% after correction to the error of preparation and readout and is limited by the temperature of the ion.
The National Institute of Information and Communications Technology in Japan is proceeding with development of an optical frequency standard using an electric quadrupole transition of Ca+ ions in a small radio-frequency trap. The single, trapped 40Ca+ ions are laser cooled to a temperature of <10 mK using extended-cavity diode lasers at 397 nm and 866 nm. In order to measure the electric quadrupole transition, the linewidth of the clock laser diode at 729 nm is reduced to ~66 Hz using an ultra-low-expansion (ULE) cavity. We observed the electric quadrupole transition with a linewidth of ~600 kHz, together with the ionic motional sidebands. We are also developing optical frequency combs without photonic fibers broadening the spectrum. The experimental is now improved in order to observe the narrower linewidth of the quadrupole transition.
Abstract The results of experiments on the implementation of single-qubit quantum gates with a single 87Rb atom in an optical dipole trap with a wavelength of 850 nm are presented. The trap is formed by a long focal-length objective lens located outside the vacuum chamber of a magneto-optical trap. An atom is detected using a resonance fluorescence signal with an sCMOS video camera. The experiments involved the trapping and confinement of a single atom at times up to 50 s, optical pumping by polarized laser radiation, microwave transitions between two hyperfine sublevels of the ground state, and the measurement of the quantum state of the atom by pushing it from the trap. Rabi oscillations are observed during the “clock” microwave transition 5S1/2(F = 2, MF = 0) → 5S1/2(F = 1, MF = 0) between two operating qubit levels at a frequency of up to 4.2 kHz, a contrast of up to 95%, and a coherence time of up to 3 ms. These oscillations correspond to the implementation of two basic single-qubit quantum operations (Hadamard gate, NOT gate) from various initial qubit states with an average fidelity of 95.2 ± 3%.
We report observation of laser excitation of a narrow, magnetic-dipole-allowed, infrared transition in a single trapped ion. Quantum jumps of a Ba+{\mathrm{Ba}}^{+}Ba+ atom were observed using a diode laser tuned in resonance with the excited-state 5d 2^{2}2D3/2{\mathit{D}}_{3/2}D3/2​--5d 2^{2}2D5/2{\mathit{D}}_{5/2}D5/2​ transition at 12.48 \ensuremath{\mu}m. Single-ion resonance line shapes were obtained and a transition frequency of \ensuremath{\nu}=24 012 033\ifmmode\pm\else\textpm\fi{}11 MHz was determined. Calculated quantum jump rates of the D-D transition for the applied laser spectral brightness yield agreement with experimentally observed values.