arXiv subjects

Necati Çelik

Publications and source records attributed to Necati Çelik.

3 recordsLinked to original sources

arXiv2026

Quantum Work Extraction via Conditional Spatial Displacements

We propose a protocol for extracting work from a coherent quantum battery state by exploiting measurement-assisted feedback mediated by a continuous-variable pointer. The scheme relies on the unitary operator $U = \exp(-i k t \, \hat{H} \otimes \hat{P}/\hbar)$, which generates entanglement between the battery's energy eigenstates and the position of an auxiliary pointer. A subsequent projective measurement of the pointer's position conditionally prepares the battery in a pure state from which work can be extracted via a feedback unitary. We analyze the protocol for a two-level quantum battery and a Gaussian pointer, computing the conditional states and the corresponding daemonic ergotropy. For the pure initial state considered, we find that the daemonic ergotropy equals the standard ergotropy for all interaction strengths, demonstrating that the measurement-assisted feedback recovers the full extractable work that would otherwise become inaccessible due to entanglement with the pointer when its degrees of freedom are traced out. The protocol thus provides a physically transparent realization of a quantum Maxwell demon, where the pointer acts as a quantum measurement ancilla whose position becomes correlated with the battery's energy. The scheme is amenable to experimental implementation in trapped-ion systems, and it contributes to the ongoing efforts to understand the role of quantum coherence and measurement in thermodynamics.

quant-ph↗

arXiv2026

Spectral-Gap Bounds and Timescales for Purity Loss in Hamiltonian--Pointer Interactions

We investigate the purity dynamics of a quantum system coupled to a continuous-variable pointer through a von Neumann-type interaction Hamiltonian of the form $\hat H_{\mathrm{int}}=g\,\hat H\otimes\hat p$. For an initially Gaussian pointer state, the interaction generates energy-dependent conditional translations whose mutual overlaps are determined explicitly by the populated spectral separations of the system Hamiltonian. After tracing out the pointer degrees of freedom, we obtain the reduced density operator and derive an exact analytical expression for the time-dependent purity. Using this expression, we establish two-sided purity bounds governed by the minimum and maximum nonzero energy gaps on the populated spectral support. These bounds provide a state-dependent spectral characterization of the loss of purity and become exact for two-level systems. We further show that the short-time decrease of purity is controlled by the Hamiltonian variance of the initial state, with $\mathcal P''(0)=-(g^2/σ^2) \operatorname{Var}_{ψ_S}(\hat H)$. In addition, an explicit sufficient timescale is derived for the purity to approach its asymptotic value within a prescribed tolerance, revealing the scaling $t_{\varepsilon}\proptoσ/(|g|Δ_{\min})$. Finally, the general results are illustrated for an equally weighted $N$-level system with an equally spaced spectrum, for which the asymptotic purity is $1/N$. The analysis clarifies the distinct roles of spectral separation, energy variance, coupling strength, and pointer width in Hamiltonian-conditioned purity loss.

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arXiv2025

Quantum-Enhanced Picostrain Sensing with Superconducting Qubits

We propose a quantum-enhanced picostrain sensor that achieves Heisenberg-limited strain sensing using superconducting qubits. A strain-sensitive qubit s Hamiltonian is coupled to the momentum quadrature of a microwave resonator, transducing mechanical strain $ε$ into amplified spatial displacements of the resonator s phase space. Using homodyne detection of the resonator field and multipartite entanglement of N qubits, the protocol achieves a strain sensitivity $Δε\sim pε$ (picostrain), two orders of magnitude better than classical sensors. The scheme integrates natively with superconducting processors, enabling in-situ diagnostic and nanoscale material characterization.

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