[Paper Review] Logical operations with single x-ray photons via dynamically-controlled nuclear resonances

Jonas Gunst, Christoph H. Keitel+1 more|arXiv (Cornell University)|Jun 1, 2015

Crystallography and Radiation Phenomena32 references20 citations

TL;DR

This paper proposes a theoretical framework for performing logical operations on single x-ray photons using dynamically controlled nuclear resonances in 57Fe. By rapidly rotating the nuclear hyperfine magnetic field, polarization-encoded x-ray qubits can be manipulated to implement single-qubit gates and a controlled-NOT gate, enabling photonic quantum logic at keV energies with potential for high spatial resolution and long coherence times.

ABSTRACT

The implementation of logical operations on polarization-encoded x-rays via resonant light-nucleus interactions is theoretically investigated. We show that by means of resonant scattering off nuclei and fast rotations of the nuclear hyperfine magnetic field to control the polarization of the output photon, single-qubit logical gates can be simulated. A second control qubit may be employed to trigger the magnetic field rotation, thus allowing several implementation choices for a controlled NOT gate for x-ray photons.

Motivation & Objective

• To enable quantum logic operations on single x-ray photons using resonant nuclear interactions.
• To overcome the challenge of controlling polarization-encoded x-ray qubits at the single-photon level.
• To demonstrate feasible implementations of one- and two-qubit quantum gates using nuclear hyperfine field control.
• To extend quantum information processing to the x-ray regime with long coherence times and high spatial resolution.
• To provide a theoretical foundation for scalable x-ray-based quantum information processing using nuclear transitions.

Proposed method

• Uses nuclear forward scattering (NFS) of x-rays on 57Fe nuclei to coherently couple x-ray polarization states to nuclear hyperfine levels.
• Employs fast, sub-4 ns rotations of the nuclear hyperfine magnetic field to dynamically control the quantization axis and redistribute collective nuclear excitation among Zeeman sublevels.
• Applies a semi-classical wave equation with perturbation theory and the slowly-varying envelope approximation to model the scattered x-ray field.
• Introduces a time-gated detection scheme to isolate the resonant nuclear response from non-resonant electronic scattering.
• Utilizes a control photon to trigger magnetic field rotation, enabling conditional logic operations such as a controlled-NOT gate.
• Models the scattered electric field amplitude as a sum over multiple scattering orders, with phase and amplitude modulated by field rotation timing and geometry.

Experimental results

Research questions

• RQ1 Can single-x-ray-photon polarization be coherently controlled via dynamically rotated nuclear hyperfine fields?
• RQ2 Is it feasible to implement universal one-qubit quantum gates using resonant nuclear scattering and field rotation?
• RQ3 Can a controlled-NOT gate be realized in the x-ray domain using a second control photon to trigger field rotation?
• RQ4 How does the timing and geometry of magnetic field switching affect the output photon polarization and gate fidelity?
• RQ5 What are the conditions under which entanglement can be generated between spatially or temporally separated x-ray modes via nuclear transitions?

Key findings

• Single-qubit logical gates can be simulated by controlling the timing and direction of nuclear hyperfine magnetic field rotation after x-ray excitation.
• A controlled-NOT gate for x-ray photons is realizable by using a second, temporally synchronized control photon to trigger the magnetic field rotation.
• The polarization of the output x-ray photon is manipulated via interference among Zeeman sublevels following field rotation, enabling arbitrary single-qubit operations.
• Theoretical modeling shows that the scattered field amplitude depends on the rotation moment t0 and the field rotation angle, allowing precise control over the output state.
• The method enables coherent processing of polarization-encoded single x-ray photons with potential for high-fidelity quantum logic operations.
• The approach leverages the long coherence time of nuclear states and the high spatial resolution of x-rays, offering advantages over optical quantum systems in certain applications.