A fiber array architecture for atom quantum computing

TL;DR

The paper presents a fiber-array architecture for atom quantum computing that enables fully independent and parallel addressing of neutral-atom qubits in a 2D optical tweezer array. By delivering trapping and Raman addressing light through the same fiber path, the approach achieves common-mode noise suppression and scalable modular replication. Experimentally, it demonstrates 10 independently addressable qubits with an average single-qubit fidelity of $0.9966(3)$ and parallel addressing of four qubits with fidelity $0.9961(4)$, along with parallel Ramsey and RB sequences across multiple sites. This architecture offers a scalable path toward time-efficient quantum algorithm execution on neutral-atom platforms, potentially reaching hundreds to thousands of qubits with further photonic integration.

Abstract

Arrays of single atoms trapped in optical tweezers are increasingly recognized as a promising platform for scalable quantum computing. In both the fault-tolerant and NISQ eras, the ability to individually control qubits is essential for the efficient execution of quantum circuits. Time-division multiplexed control schemes based on atom shuttling or beam scanning have been employed to build programmable neutral atom quantum processors, but achieving high-rate, highly parallel gate operations remains a challenge. Here, we propose a fiber array architecture for atom quantum computing capable of fully independent control of individual atoms. The trapping and addressing lasers for each individual atom are emitted from the same optical waveguide, enabling robust control through common-mode suppression of beam pointing noise. Using a fiber array, we experimentally demonstrate the trapping and independent control of ten single atoms in two-dimensional optical tweezers, achieving individually addressed single-qubit gate with an average fidelity of 0.9966(3). Moreover, we perform simultaneous arbitrary single-qubit gate on four randomly selected qubits, resulting in an average fidelity of 0.9961(4). Our work paves the way for time-efficient execution of quantum algorithms on neutral atom quantum computers.

Figures (8)

• Figure 1: Experimental scheme.a, Basic experimental setup for the trapping, manipulation, and detection of single atom arrays. Each optical module is used for trapping and addressing an individual atom. The optical tweezers are generated using an optical fiber array. Multi-channel trapping beams are emitted from the end face of the fiber array and, after collimation and expansion, are focused by a objective (NA = 0.7) into the vacuum chamber, creating an optical trap array. The addressing beams are focused onto the trap array along the same optical path as the trapping beams. Atom fluorescence signals are collected by the same objective and imaged onto an sCMOS camera after being reflected by a dichroic mirror. b, The cross-section of the fiber array consists of 64 single-mode fibers, each with cladding reduced to $40\,\mu\text{m}$ at the ends. The 10 fibers enclosed in the dashed box are chosen for this experiment. c, Averaged fluorescence images of the single-atom array, taken with an exposure time of 50 ms. d, A schematic showing optical setup in the optical module. A single $830\,$nm trapping beam and a pair of $795\,$nm addressing Raman beams each pass through an AOM before being combined into the same SM fiber using a WDM. e, Histogram of collected photons for one of the traps. Two distinct peaks indicate the presence of one atom (right peak) and no atom (left peak) in the trap.
• Figure 2: Individual addressing of single-atom qubit arrays.a, Energy level schematic for the qubits. Qubits are encoded in the two hyperfine ground states of ${}^{87}\mathrm{Rb}$ atoms: $|0\rangle\equiv |5S_{1/2},F=2, m_F=0\rangle$ and $|0\rangle\equiv |5S_{1/2},F=1, m_F=0\rangle$, which are coupled by a two-photon Raman transition featuring a single-photon detuning of $2\pi \times 200\,\text{GHz}$ relative to the $5P_{1/2}$ manifold. b, Optical configuration for Raman laser beams. Two coherent laser beams, one modulated by an fEOM and the other unmodulated, are each split into ten paths. Each pair of split beams ($R_1$ and $R_2$) pass through an AOM from opposite sides, obtaining +1 and -1 order diffractions respectively. They are then combined into a single SM PM fiber with identical polarization. The driving frequencies for the fEOM and AOM are set at 7.054 GHz and 100 MHz, respectively. The +1 sideband of the fEOM on $R_2$, in combination with $R_1$, forms a pair of Raman beams with a frequency difference of 6.834 GHz. c, Optical methods for switching laser polarization and expanding the addressing spot. The driving voltage amplitude of the LCVR is varied to meet the laser polarization requirements for different experimental phase. During the atom loading, PGC, and detection phases, the polarization is set to linear. In the addressing phase, it is switched to circular. A window featuring a 1 mm diameter central aperture, which is highly reflective at $795\,$nm and highly transmissive at $830\,$nm, is inserted into the optical path to enlarge the beam waist of the addressing spot. d, Rabi oscillation of the 10 single atoms when addressing one single atom. The upper panel displays the Rabi oscillations of a specific qubit (qubit 7), driven by a Raman pulse, whereas the lower panel depicts the evolution of other qubits subjected to a longer Raman pulse.
• Figure 3: RB of individually addressed single-qubit gates. The upper panel shows RB experiment on one of the qubits (qubit 7), from which a fidelity of 0.9971 (2) for individually addressed single-qubit gates was extracted. The lower panel displays a site-by-site analysis of average single-qubit fidelities, which vary between 0.995 and 0.998.
• Figure 4: Simultaneous Ramsey experiment on the entire array.a, The Ramsey sequence comprises two $\pi/2$ pulses with a phase-shift pulse inserted between them to alter the phase of the second $\pi/2$ pulse. At each site, the Ramsey sequence is configured with unique two-photon frequencies $f_i$ and phase offsets $\phi_i$. b, 10 single-atom qubits undergo simultaneous Ramsey oscillations, each manifesting distinct frequencies {5.5 kHz, 5 kHz, 4.5 kHz, 4 kHz, 3.5 kHz, 3 kHz, 2.5 kHz, 2 kHz, 1.5 kHz, 1 kHz} and initial phases {0, $\pi/2$, -$\pi/2$, $\pi/4$, $-\pi/4$, $\pi/6$, $-\pi/6$, $\pi/8$, $-\pi/8$, $\pi/10$}.
• Figure 5: Parallel RB on four arbitrary qubits.a, Parallel addressing of four arbitrary single-atom qubits. Bottom: The Rabi oscillation of qubit 6, which exhibits rapid dephasing. b, Simultaneous RB experiments on four targeted qubits by applying an independent sequence of Clifford gates to each qubit. The fidelity of parallel-addressed single-qubit gates ranges from 0.995 to 0.997, closely approximating that of individually addressed single-qubit gates.