Yb³⁺ Spectroscopy and Quantum-Control Testbed

Project Overview

This project explores the optical and microwave response of Yb³⁺-doped crystals using an accessible, modular laboratory setup.

The experimental platform combines:

• infrared laser excitation;
• microwave-frequency sweeps and pulse control;
• an externally applied magnetic field;
• InGaAs photodiode detection;
• DAQ and FPGA-based timing;
• Python, LabVIEW and Qiskit-based data-processing tools.

The current build should be understood as a spectroscopy and control testbed, not as a completed quantum computer.

Its purpose is to characterize the hardware, establish a reliable measurement chain and investigate whether repeatable spin-dependent or coherence-related signals can be detected in the selected Yb³⁺ material.

Current Project Status

A hardware platform is being assembled around Yb³⁺-doped crystal samples, infrared laser modules, a microwave signal generator, magnetic-field control, an InGaAs detector and a USB DAQ.

The software currently includes Qiskit simulations of multi-qubit circuits. These simulations are used to develop control logic, pulse sequences and data-handling workflows. They do not represent physical qubits already operating in the crystal.

The analog voltage measured by the photodiode is treated as an experimental optical signal. It will only be interpreted as evidence of a quantum or spin transition after appropriate calibration, control measurements and statistical analysis.

The immediate experimental work focuses on:

• measuring the optical spectrum and detector noise floor;
• characterizing laser stability and wavelength;
• calibrating the microwave and magnetic-field systems;
• testing whether microwave-frequency sweeps produce repeatable optical changes;
• investigating pulse-dependent responses;
• separating genuine sample responses from thermal, electrical and optical artifacts.

Experimental Goals

The project aims to develop a documented platform that can be used to investigate:

1. optical absorption and emission from Yb³⁺-doped materials;
2. magnetic-field-dependent spectral changes;
3. microwave-driven transitions;
4. optically detected magnetic resonance, where supported by the material and transition;
5. pulse sequences associated with Rabi, Ramsey, T₁ and T₂ measurements;
6. integration between laboratory instruments and quantum-control software.

These measurements require considerably more than observing a change in photodiode voltage. A candidate signal must be repeatable, correlated with a controlled experimental parameter and distinguishable from the measured noise and background response.

The Role of BSM-SG

BSM-SG is included in this project as a hypothesis-generating structural model.

It is not used as a replacement for quantum mechanics, established spectroscopy or conventional spin-Hamiltonian analysis. It does not remove the need for stable lasers, calibrated microwave sources, temperature control or careful experimental validation.

The proposed role of BSM-SG is to generate candidate predictions concerning:

• resonance-frequency regions;
• preferred magnetic-field orientations;
• possible structural anisotropies;
• relationships between nuclear structure and magnetic response;
• material and isotope selection;
• experimental parameter ranges worth investigating.

Where possible, these predictions will be expressed quantitatively before the corresponding measurements are performed.

The experimental results will then be compared with both:

• conventional crystal-field and spin-Hamiltonian models; and
• the additional predictions proposed by BSM-SG.

A familiar effect such as an ODMR resonance, Rabi oscillation or Ramsey fringe would not by itself validate BSM-SG. Such effects are already described by established quantum theory.

For BSM-SG to provide additional scientific value, it must produce a specific, testable prediction that is confirmed experimentally and performs at least as well as, or better than, the conventional...