We investigate non-Markovian quantum memory in a negatively charged nitrogen-vacancy (NV) center strain-coupled to a quantized mechanical mode. From the spin-1 NV Hamiltonian and the C_3v spin--strain interaction, we derive an effective qubit--phonon model with transverse exchange and longitudinal phase-modulation couplings. The open dynamics is described by a GKSL master equation, and memory in the reduced qubit channel is characterized using trace-distance backflow for the orthogonal reference pair │±〉= (│0〉± │-1〉) / √2 and the Rivas--Huelga--Plenio (RHP) CP-divisibility criterion. At resonance, the reference-pair BLP backflow follows transverse > hybrid > longitudinal, whereas the extrapolated RHP quantity follows hybrid > transverse >> longitudinal. Adding g_z / ω_m = 0.10 to the transverse baseline g⊥ / ω_m = 0.20 reduces the reference-pair backflow by 8.61% while increasing the RHP quantity by approximately 78.65%. This opposite response is traced to the distinct roles of coherent exchange and longitudinal phase modulation in distinguishability recovery and full-channel CP-indivisibility. The same ordering contrast persists over the sampled detuning interval, whereas thermal occupation can modify the BLP hierarchy and induce isolated noninvertibility of the reduced dynamical map for some exchange-containing regimes. Numerical validation and convergence tests confirm the robustness of the principal resonance result and delineate the validity of the inverse-based RHP construction.
We investigate non-Markovian quantum memory in a negatively charged nitrogen-vacancy (NV) center strain-coupled to a quantized mechanical mode. From the spin-1 NV Hamiltonian and the C_3v spin--strain interaction, we derive an effective qubit--phonon model with transverse exchange and longitudinal phase-modulation couplings. The open dynamics is described by a GKSL master equation, and memory in the reduced qubit channel is characterized using trace-distance backflow for the orthogonal reference pair │±〉= (│0〉± │-1〉) / √2 and the Rivas--Huelga--Plenio (RHP) CP-divisibility criterion. At resonance, the reference-pair BLP backflow follows transverse > hybrid > longitudinal, whereas the extrapolated RHP quantity follows hybrid > transverse >> longitudinal. Adding g_z / ω_m = 0.10 to the transverse baseline g⊥ / ω_m = 0.20 reduces the reference-pair backflow by 8.61% while increasing the RHP quantity by approximately 78.65%. This opposite response is traced to the distinct roles of coherent exchange and longitudinal phase modulation in distinguishability recovery and full-channel CP-indivisibility. The same ordering contrast persists over the sampled detuning interval, whereas thermal occupation can modify the BLP hierarchy and induce isolated noninvertibility of the reduced dynamical map for some exchange-containing regimes. Numerical validation and convergence tests confirm the robustness of the principal resonance result and delineate the validity of the inverse-based RHP construction.
Abstract Digital quantum simulation of open quantum systems has produced a range of methods for reproducing non-Markovian dynamics, including pseudomode embeddings, the hierarchical equations of motion, and collision models. These methods are validated against populations, coherences, or spectra. They are not validated against the quantities that define memory itself, and the behavior of those quantities under the pressures of a real simulation is largely unexamined. We study three such pressures. First, a single-qubit mode encoding misrepresents the Breuer-Laine-Piilo (BLP) measure with an error whose sign flips between regimes: it fabricates memory at strong coupling, by about a factor of 2.6 over the converged value, and it erases memory at moderate temperature. The Rivas-Huelga-Plenio (RHP) measure corroborates the temperature-driven destruction, while at strong coupling it is numerically unstable and does not track the BLP result. We derive a cross-validated rule for the required Fock dimension that collapses both regimes onto the occupied number extent, d req ≈ ⌈⟨n⟩+c σ n ⌉+1, and we show that the constant must be calibrated on super-Poissonian statistics. Second, using the exact noisy measure as computable ground truth, we show that the raw finite-shot estimate of the BLP measure can nearly double the true value under realistic noise. We provide a debiased estimator that is validated near-unbiased in that regime, together with a Markovian null-floor control that ports to hardware. Third, temporally correlated device noise is conflated with physical memory by the measure. A resource-fair comparison finds that a pseudomode and an ancilla-train collision model reach parity at equal qubit cost for a single-Lorentzian bath. Every result is simulator-based, validated against an exact reference, and reproducible from recorded data. We make no claim of quantum advantage.
Abstract The electron–phonon interaction is a cornerstone of condensed matter physics, playing a pivotal role in the properties of solid-state systems. When localized electronic states are coupled to lattice vibrations, phonons can induce memory effects. This study explores the non-equilibrium dynamics of a negatively charged silicon-vacancy center in diamond, analyzing the effects of both single phonon mode and structured phonon environment. Using numerical simulations and theoretical analysis, we employ trace distance as a metric to identify and understand memory effects in the transient dynamics and non-Markovian evolution. We systematically investigate the impact of longitudinal and transverse magnetic fields, phonon coupling strengths, Fock states, localized vibrations, and temperature on memory effects in this solid-state system. Our findings provide deeper insights into the interplay between electronic states and phonon environments, offering a comprehensive understanding of the conditions that govern the backflow of information in quantum solid-state devices.
In a diamond, the mechanical vibration-induced strain can lead to interaction between the mechanical mode and the nitrogen-vacancy (NV) centers. In this work, we propose to utilize the strain-induced coupling for the quantum non-demolition (QND) single phonon measurement and memory in a diamond. The single phonon in a diamond mechanical resonator can be perfectly absorbed and emitted by the NV centers ensemble (NVE) with adiabatically tuning the microwave driving. An optical laser drives the NVE to the excited states, which have much larger coupling strength to the mechanical mode. By adiabatically eliminating the excited states under large detuning limit, the effective coupling between the mechanical mode and the NVE can be used for QND measurement of the single phonon state. Under realistic experimental conditions, we numerically simulate the scheme. It is found that the fidelity of the absorbing and emitting process can reach a much high value. The overlap between the input and the output phonon shapes can reach 98.57%.
A fully functional quantum computer must contain at least two important components: a quantum memory for storing and manipulating quantum information and a quantum data bus to securely transfer information between quantum memories. Typically, a quantum memory is composed of a matter system, such as an atom or an electron spin, due to their prolonged quantum coherence. Alternatively, a quantum data bus is typically composed of some propagating degree of freedom, such as a photon, which can retain quantum information over long distances. Therefore, a quantum computer will likely be a hybrid quantum device, consisting of two or more disparate quantum systems. However, there must be a reliable and controllable quantum interface between the memory and bus in order to faithfully interconvert quantum information. The current engineering challenge for quantum computers is scaling the device to large numbers of controllable quantum systems, which will ultimately depend on the choice of the quantum elements and interfaces utilized in the device. In this thesis, we present and characterize a hybrid quantum device comprised of single nitrogen-vacancy (NV) centers embedded in a high quality factor diamond mechanical oscillator. The electron spin of the NV center is a leading candidate for the realization of a quantum memory due to its exceptional quantum coherence times. On the other hand, mechanical oscillators are highly sensitive to a wide variety of external forces, and have the potential to serve as a long-range quantum bus between quantum systems of disparate energy scales. These two elements are interfaced through crystal strain generated by vibrations of the mechanical oscillator. Importantly, a strain interface allows for a scalable architecture, and furthermore, opens the door to integration into a larger quantum network through coupling to an optical interface.There are a few important engineering challenges associated with this device. First, there have been no previous demonstrations of a strain-mediated spin-mechanical interface and hence the system is largely uncharacterized. Second, fabricating high quality diamond mechanical oscillators is difficult due to the robust and chemically inert nature of diamond. Finally, engineering highly coherent NV centers with a coherent optical interface in nanostructured diamond remains an outstanding challenge. In this thesis, we theoretically and experimentally address each of these challenges, and show that with future improvements, this device is suitable for future quantum-enabled applications. First, we theoretically and experimentally demonstrate a dynamic, strain-mediated coupling between the spin and orbital degrees of freedom of the NV center and the driven mechanical motion of a single-crystal diamond cantilever. We employ Ramsey interferometry to demonstrate coherent, mechanical driving of the NV spin evolution. Using this interferometry technique, we present the first demonstration of nanoscale strain imaging, and quantitatively characterize the previously unknown spin-strain coupling constants. Next, we use the driven motion of the cantilever to perform deterministic control of the frequency and polarization dependence of the optical transitions of the NV center. Importantly, this experiment constitutes the first demonstration of on-chip control of both the frequency and polarization state of a single photon produced by a quantum emitter. In the final experiment, we use mechanical driving to engineer a series of spin ``clock" states and demonstrate a significant increase in the spin coherence time of the NV center. We conclude this thesis with a theoretical discussion of prospective applications for this device, including generation of non-classical mechanical states and spin-spin entanglement, as well as an evaluation of the current limitations of our devices, including a possible avenues for improvement to reach the regime of strong spin-phonon coupling.
We present a falsifiable, measurement-driven protocol to reconstruct a triadic temporal structure Ψ(t) = (t,ϕ,χ) in a single nitrogen-vacancy (NV) center spin qubit under controlled driving and engineered environments. The phase channel ϕ(t) is extracted from Ramsey interferometry (including geometric phase contributions), while the memory channel χ(t) is reconstructed via dynamical decoupling (DD) spectroscopy and process-tensor tomography. We introduce a data-defined regime diagnostic vector ∆Φ(t) computed directly from (i) phase residuals in Ramsey fringes, (ii) kernel-based memory strength, and (iii) a CP-divisibility (RHP) non-Markovianity witness derived from multi-time process reconstruction. To combine components with different physical scales, we replace unweighted norms by a covariance-weighted regime score J(t) = ∆Φ(t)TΣ−1∆Φ(t) calibrated from baseline controls. The framework is explicitly conservative: it does not modify unitary quantum mechanics, does not invoke new particles or retrocausal signalling, and reduces to standard Markovian open-system dynamics in a controlled recovery limit. We provide an experimental matrix with explicit falsification triggers, a methods page with concrete pulse sequences (Ramsey, CPMG, XY8), and null tests compatible with room-temperature NV platforms.
The electron-phonon interaction is one of the most fundamental mechanisms in condensed matter physics. Phonons can induce memory effects in solid-state platforms when localized electronic states interact with lattice vibrations in non-unitary dynamical maps. In this work, we demonstrate how single-mode and structured phonon environments can give rise to non-Markovian dynamics of an individual negatively charged silicon-vacancy center in diamond. Using trace distance as a quantifier via numerical simulations and theoretical calculations, we identify the physical conditions for emerging and understanding non-Markovian behavior in diverse scenarios. Most importantly, we investigate the influence of magnetic fields (longitudinal and transverse), phonon couplings, Fock states, and temperature to understand how these factors influence memory effects in this solid-state device.