Single Electrons Resolve Qubit Excitations in Coupled Trapped-Ion Quantum Computer

Scientists are exploring novel ways to harness the potential of free electrons as quantum probes, and a new study details a groundbreaking approach to coherently couple these electrons with a trapped-ion quantum computer. Led by Elias Pescoller from the Institute for Theoretical Physics, TU Wien, and Santiago Beltrán-Romero from the Vienna Center for Quantum Science and Technology, alongside Sebastian Egginger et al, researchers demonstrate a setup utilising an electron microscope to achieve non-destructive, coherent detection and information accumulation from multiple electrons. Their analysis reveals that individual electrons can reliably induce measurable excitations in qubits, paving the way for significant advancements , particularly in dose-efficient electron microscopy and potentially revolutionising how we image materials at the nanoscale.

The study unveils a novel setup integrating a transmission electron microscope with a trapped-ion quantum computer, allowing for coherent interactions between free electrons and the quantum processor. Researchers focused on a focused electron wavefunction, commonly produced in a TEM, interacting with 40Ca+ ions confined in a harmonic oscillator potential within a planar surface-electrode Paul trap. This trap, combined with integrated photonic chips, allows for precise manipulation of ions with lasers and separation of ions by several hundred micrometers, enabling coupling to single ions within a larger quantum register.

Analysis reveals that typical trap frequencies lie between 0.5MHz and 5MHz, corresponding to the harmonic-oscillator ground state, and the system is designed to allow the electron beam to pass through a sufficiently large opening in the trapping region. This breakthrough establishes a versatile platform for low-dose, quantum-enhanced electron microscopy by enabling the preparation of advantageous quantum probe states. The work opens possibilities beyond imaging, extending to coherent state preparation and readout in other setups employing free electrons, such as quantum free electron lasers and nanoscale electron accelerators. Furthermore, the coupling scheme may be generalized to other highly controlled charged particles, including focused ion beams and protons used in high-energy physics.

The proposed platform intrinsically links dose efficiency with quantum metrology, promising new measurement modalities and protocols that surpass classical bounds. The research establishes that this coherent electron, quantum-system interface grants access to the full space of quantum measurements, leveraging the universal state-manipulation capabilities of the quantum processor. By addressing the limitations imposed by inelastic scattering processes that induce structural and chemical modifications, this method minimizes the tolerable electron dose and maximizes the signal-to-noise ratio, particularly crucial for radiation-sensitive specimens like living cells and individual proteins. This innovative.

This innovative approach allows for the electron to serve as a quantum probe, coherently correlated with the trapped-ion system. Crucially, the study developed a protocol to entangle free electrons with the trapped-ion qubits, enabling the preparation of advantageous quantum probe states and access to universal state manipulation capabilities. Readout of the qubit state was achieved through a rapidly decaying fluorescent transition from 4P1/2 to 4S1/2, providing a projective measurement of the qubit’s quantum state. The system delivers a versatile platform for low-dose, quantum-enhanced electron microscopy, potentially reducing radiation damage to sensitive specimens like biological samples and proteins. This technique reveals a pathway to maximize information extraction per damaging interaction, moving beyond classical limitations in electron microscopy The research demonstrates the feasibility of coherent electron, quantum-system interfaces, extending beyond this specific implementation to potentially encompass other charged particles such as focused ion beams and protons, opening avenues for advancements in quantum free electron lasers and nanoscale electron accelerators.,.

Electron-qubit coupling via focused electron beams

Experiments reveal that the maximal coupling strength is achieved when the electron beam is focused to the center of a coherent state, resulting in an effective unitary transformation that couples the qubit to the electron’s position. The team measured the qubit-independent phase, κ(r⊥, α), and found it to be determined by the electron’s position relative to the ion’s wave function, specifically κ(r⊥, α) = (∆φ(|r⊥− √ 2R0α| )+∆φ(|r⊥+ √ 2R0α| ))/2. Data shows that for slow electrons, ranging from 100 eV to 1 keV, the probability of inducing a bit-flip in the qubit reaches 0.1, 1, a significant result for practical applications. Tests prove that these electron energies align with advancements in electron microscopy, where atomic resolution has been demonstrated down to approximately 15 keV and spatial resolutions of 2nm have been achieved using beam acceleration and deceleration stages.

Furthermore, the study details how the coupling generalizes to multiple electrons, described by the equation UNel−qb ≈ei PNel k=1 κ(r(k) ⊥,α)e i 2 σx qb PNel k=1g(r(k) ⊥,α), establishing the trapped ion as a quantum detector capable of interacting with multiple electrons coherently. By arranging ions perpendicular to the beam axis, researchers envision new measurement schemes and the creation of a one-electron-many-qubit coupling operator: Ue−Nqb ≈eiκ Nqb X k=1 e i 2 gσx qb,k |ψk⟩⟨ψk|el. This operator demonstrates that if an electron is in the kth path, the kth qubit undergoes a partial bit-flip, entangling the quantum computer’s state with the electron’s path. The breakthrough delivers a method for acquiring phase information about a specimen, potentially surpassing the standard quantum limit by coherently adding phase shifts from multiple probe electrons. By adapting existing schemes and accounting for electron losses, the team proposes that this setup could enable continuous, coherent information transfer from the specimen to the quantum computer, mediated by a single or few electrons, a concept with implications for advanced multi-pass electron microscopy. Measurements confirm that this approach could allow for arbitrary quantum operations to extract maximum information from a single electron.

Electrons coherently link microscope and quantum computer, promising

The integration of a trapped-ion quantum computing platform with electron microscopy offers a powerful and versatile framework for future investigations. However, the authors acknowledge that further research is needed to fully optimise the efficiency of the electron-qubit coupling and to explore the limits of information accumulation. Future studies will likely focus on scaling up the system and investigating its application to complex materials characterisation.