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arXiv:2605.18108

Quantum-Battery-Powered Geometric Landau-Zener Interferometry

Borhan Ahmadi

quant-phSubmitted May 18, 2026• Announced May 19, 2026• 0 citations
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Abstract

Classical microwave drives are usually treated as ideal phase-coherent work sources for superconducting-qubit control. What if such a drive is replaced by a finite quantum battery. As a demanding benchmark, we consider echo-refocused geometric Landau--Zener interferometry powered by a single quantized bosonic mode. The qubit--battery dynamics are described by a Jaynes--Cummings Hamiltonian, while the echo pulse is retained as a qubit-only refocusing operation that cancels the dynamical phase. In the macroscopic coherent-state limit, the usual classical geometric interferometer is recovered. At finite mean photon number, however, the Jaynes--Cummings coupling generates photon-number-resolved avoided crossings with gaps $Ω_n=2g\sqrt{n}$. The qubit-only echo redistributes amplitudes between neighboring excitation sectors, so the finite-battery protocol is not a single classical interferometer but a coherent sector-resolved quantum evolution. This produces contrast loss, interferogram distortions, and measurable battery back-action. We further show that reducing photon-number fluctuations alone is not sufficient: geometric control requires a first-order phase reference. Geometric Landau--Zener interferometry therefore provides a practical benchmark for certifying phase-coherent quantum-battery energy.

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Classical microwave drives are usually treated as ideal phase-coherent work sources for superconducting-qubit control. What if such a drive is replaced by a finite quantum battery. As a demanding benchmark, we consider echo-refocused geometric Landau--Zener interferometry powered by a single quantized bosonic mode. The qubit--battery dynamics are described by a Jaynes--Cummings Hamiltonian, while the echo pulse is retained as a qubit-only refocusing operation that cancels the dynamical phase. In the macroscopic coherent-state limit, the usual classical geometric interferometer is recovered. At finite mean photon number, however, the Jaynes--Cummings coupling generates photon-number-resolved avoided crossings with gaps Ωn=2gnΩ_n=2g\sqrt{n}Ωn​=2gn​. The qubit-only echo redistributes amplitudes between neighboring excitation sectors, so the finite-battery protocol is not a single classical interferometer but a coherent sector-resolved quantum evolution. This produces contrast loss, interferogram distortions, and measurable battery back-action. We further show that reducing photon-number fluctuations alone is not sufficient: geometric control requires a first-order phase reference. Geometric Landau--Zener interferometry therefore provides a practical benchmark for certifying phase-coherent quantum-battery energy.
Geometric quantum manipulation and Landau-Zener interferometry have been separately explored in many quantum systems. In this Letter, we combine these two approaches to study the dynamics of a superconducting phase qubit. We experimentally demonstrate Landau-Zener interferometry based on the pure geometric phases in this solid-state qubit. We observe the interference caused by a pure geometric phase accumulated in the evolution between two consecutive Landau-Zener transitions, while the dynamical phase is canceled out by a spin-echo pulse. The full controllability of the qubit state as a function of the intrinsically robust geometric phase provides a promising approach for quantum state manipulation.
Quantum batteries have been proposed as locally precharged work sources for superconducting quantum technologies, suggesting a route to reduce continuously supplied microwave drives. Here we ask whether the pump tone of a quantum-limited parametric amplifier can be replaced, or strongly duty-cycled, by a finite bosonic quantum battery. Quantizing the pump of a nondegenerate parametric amplifier exposes a resource distinction hidden in the classical description: stored pump energy can generate signal-idler photons, but pump phase coherence is required to generate a phase-locked amplifier field. In a closed trilinear model, coherent and phase-randomized coherent pumps with the same photon-number distribution produce comparable pair numbers, yet only the coherent pump produces anomalous two-mode coherence and an EPR-squeezed interference dip. Including leakage, we collect the emitted fields into cascaded temporal modes. At matched collector bandwidth, the coherent pump gives Imin⁡(f)=0.553I_{\min}^{(f)}=0.553Imin(f)​=0.553, whereas the phase-randomized pump gives Imin⁡(f)=1.94I_{\min}^{(f)}=1.94Imin(f)​=1.94 at nearly identical collected energy. Weak amplitude squeezing slightly improves the dip by reducing finite-pump number fluctuations while preserving the coherent displacement. Thus battery-powered parametric amplification requires phase-coherent stored energy, possibly assisted by number-noise reduction, rather than stored energy alone.
We perform Landau-Zener-St\"uckelberg interferometry on a single electron GaAs charge qubit by repeatedly driving the system through an avoided crossing. We observe coherent destruction of tunneling, where periodic driving with specific amplitudes inhibits current flow. We probe the quantum dot occupation using a charge detector, observing oscillations in the qubit population resulting from the microwave driving. At a frequency of 9 GHz we observe excitation processes driven by the absorption of up to 17 photons. Simulations of the qubit occupancy are in good agreement with the experimental data.
Bosonic modes provide a promising platform for quantum batteries as a result of their unbounded energy spectrum. However, the energy that can be stored during a coherent charging process is limited due to coherent oscillations between the charger and battery. In this work, we show that by introducing a slow quench in the interaction between a coherently driven charger mode and a quadratic oscillator battery, the maximum stored energy and maximum battery power scale algebraically with the quench duration, with exponents controlled by the ramp profile. This finding implies that, quite counterintuitively, slower quenches lead to faster charging. Such a quench suppresses coherent energy oscillations between the battery and the charger, allowing an unbounded increase in power. We further show that, in the ideal closed protocol, the stored energy is fully extractable as ergotropy, while charger dissipation converts the algebraic enhancement into a finite-time scaling window with an optimal quench duration. We also show that the temporal-extensive scaling occurs in a broader context by mapping the system to a coherently driven Tavis-Cummings battery. Finally, we discuss experimentally accessible signatures in superconducting circuit quantum electrodynamics and organic microcavity platforms.
We explore coherent ergotropy extraction in quantum batteries from a resource-geometric point of view. For an initial state ρρρ, we quantify the coherent extraction process by the coherent ergotropy Ec(ρ)\mathcal{E}_c(ρ)Ec​(ρ) and the coherent extraction distance Dcext(ρ)D_c^{\rm ext}(ρ)Dcext​(ρ) between the active state σρσ_ρσρ​ and the passive state PρP_ρPρ​. This defines the geometric power capacity Πc(ρ)=Ec(ρ)/Dcext(ρ)Π_c(ρ)=\mathcal{E}_c(ρ)/D_c^{\rm ext}(ρ)Πc​(ρ)=Ec​(ρ)/Dcext​(ρ), which measures the coherent ergotropy released unit minimal unitary distance. We prove that, for any driving Hamiltonian satisfying ∥Vt∥≤ν\|V_t\|\leqν∥Vt​∥≤ν, the actual coherent discharging power is bounded by Pcext(ρ;Vt)≤νΠc(ρ)P_c^{\rm ext}(ρ;V_t)\leq νΠ_c(ρ)Pcext​(ρ;Vt​)≤νΠc​(ρ), showing that Πc(ρ)Π_c(ρ)Πc​(ρ) is a capacity under unit driving norm rather than the power of a particular protocol. General bounds on Πc(ρ)Π_c(ρ)Πc​(ρ) are derived by combining relative entropy bounds on coherent ergotropy with geometric bounds on the coherent extraction distance. We also formulate coherence measure induced bounds and protocol-corrected capacities involving the effective speed of a given Hamiltonian. Qubit and qutrit examples demonstrate that Πc(ρ)Π_c(ρ)Πc​(ρ) captures a resource-geometric feature of coherent discharging beyond coherent ergotropy or coherence measures alone.
We demonstrate Mach-Zehnder-type interferometry in a superconducting flux qubit. The qubit is a tunable artificial atom, the ground and excited states of which exhibit an avoided crossing. Strongly driving the qubit with harmonic excitation sweeps it through the avoided crossing two times per period. Because the induced Landau-Zener transitions act as coherent beamsplitters, the accumulated phase between transitions, which varies with microwave amplitude, results in quantum interference fringes for n = 1 to 20 photon transitions. The generalization of optical Mach-Zehnder interferometry, performed in qubit phase space, provides an alternative means to manipulate and characterize the qubit in the strongly driven regime.