{"id":"acdd8bb2-39df-4f6f-899a-08cc93becb96","arxiv_id":"2505.21157","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"A pair of coupled acoustic cavities with active electronic feedback reproduces quantum-like two-level dynamics, including Rabi oscillations, Ramsey interference, Floquet loss suppression, and spin echo.","lead":"This paper builds a low-cost acoustic two-level system from two coupled resonators and uses programmable electronic feedback to mimic qubit behavior. It demonstrates Rabi oscillations, Ramsey interference, Floquet driving, and spin echo on the Bloch sphere using sound waves.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The central claim requires that the same active feedback circuits used to synthesize the Hamiltonian do not corrupt the state readout; the paper provides no independent calibration of this, so 'full Bloch-sphere control' is not yet established.","rationale":"The reader's conditional verdict already identifies measurement backaction and feedback crosstalk as the weakest assumption. My stress-test agrees and sharpens it: the reported 'real-time monitoring' appears to draw on the same active loops that implement the Hamiltonian, so the reconstructed Bloch vector may be a servo response rather than an independent record of the cavity state. This is load-bearing because the central claim is not just that the device can be programmed to produce certain outputs, but that it realizes genuine Hamiltonian-driven Bloch dynamics. If the readout is not independent, the theory-experiment agreement in every figure could be tautological. The proposed test is concrete and would settle the concern: independent physical probes of the acoustic field, compared with the in-loop signals, plus an open-loop control check. I do not see a basis to reject the paper outright; the work is internally plausible and the protocol descriptions are coherent, so the appropriate verdict remains conditional pending this validation and the supporting data/code release already requested by the reader.","tokens_in":9263,"tokens_out":5057,"duration_ms":63548,"concrete_test":"Perform a two-channel validation while running the Rabi and Ramsey sequences: measure the cavity amplitudes and phases both from the in-loop feedback signals used for reconstruction and from an independent calibrated microphone or laser-vibrometer probe on each cavity, using a separate acquisition path. Also repeat one gate, such as the pi pulse, with the active feedback temporarily opened at low gain. If the two readouts disagree by more than the quoted noise floor, or if the open-loop behavior does not match Eq. (1), the claimed independent Bloch-state reconstruction fails and the 'full Bloch-sphere control' claim needs to be weakened.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's central claim is that the observed trajectories are Bloch dynamics generated by the programmable Hamiltonian in Eq. (1). This requires that the measured mode amplitudes and relative phases used for reconstruction are independent probes of the cavity state, not control-loop setpoints. The Methods describe voltage-controlled amplifiers and programmable phase shifters inside active feedback loops but do not describe a separate calibrated readout channel; the same loops that set gamma_1,2(t) and kappa(t) appear to be the source of the reported C1/C2 amplitudes. In a high-gain servo, the monitored signal is forced to the programmed waveform, so agreement with theory would be the expected tracking response rather than evidence for the Hamiltonian. The absence of any open-loop calibration, error bars, or independent readout makes this the least secured link between the data and the core claim.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports a classical acoustic two-level system built from two electromagnetically coupled cavities with active feedback control over detuning, loss rates, and inter-cavity coupling. By programming these parameters in time, the authors demonstrate textbook single-qubit control primitives—Rabi oscillations, chiral Bloch-sphere trajectories, Ramsey interference, Floquet-driven decay suppression, and spin echo rephasing—and claim full Bloch-sphere control. The theoretical model is a two-level Schrödinger-type equation with a time-dependent non-Hermitian Hamiltonian, and the plotted theory curves appear to be direct solutions with no free parameters fitted to the central data. The manuscript is clearly written and the protocols are standard, but the experimental validation raises concerns about the independence of the measurement from the feedback control that synthesizes the Hamiltonian.","tokens_in":9431,"tokens_out":6217,"duration_ms":74241,"significance":"If the results hold, this is a low-cost, room-temperature classical platform for visualizing and teaching Bloch dynamics and coherent control concepts, with potential applications in transient acoustic field shaping. The paper's strengths include explicit parameter-free theoretical predictions for Rabi, Ramsey, and echo sequences, and a clear demonstration of Floquet modulation as a means to offset dissipation. However, the significance is moderate rather than transformative: the physics is classical wave mechanics with active feedback, not a genuine quantum system, and the central claim of 'complete Bloch sphere control' is not supported by a rigorous independent readout or by quantitative fidelity metrics. The paper would be acceptable in a specialist acoustics or applied-physics venue if the experimental methodology is hardened.","major_comments":[{"comment":"All experimental data are presented without error bars, repeated-run statistics, or a quantified measure of theory-experiment agreement. Claims of 'excellent agreement' (e.g., Fig. 3b) are visual assertions only. At minimum, the authors should report the standard deviation over multiple trials for representative traces, and provide a fidelity metric such as the trace distance or overlap between measured and theoretical Bloch vectors at each time point. Without this, it is impossible to assess whether the observed deviations are within experimental uncertainty or reveal a systematic discrepancy.","section":"Results, Fig. 1c, Fig. 3b, Fig. 4b"},{"comment":"The theoretical phase diagram and the modified exceptional-point condition predict a specific threshold in δγ for the onset of net gain. The experimental confirmation, however, only shows a qualitative comparison of the static versus Floquet-modulated time traces (Fig. 2d) and normalized power decay (Fig. 2e). There is no measurement of the amplification rate as a function of δγ or T, and no identification of the threshold crossing. The section's conclusion that Floquet engineering 'reduces the gain threshold' is therefore not directly validated by the presented data. I recommend measuring the time-domain growth/decay rate for several values of δγ around the predicted threshold and comparing with the theory curve.","section":"Floquet dynamics, Fig. 2b–2e"},{"comment":"The paper claims 'complete Bloch sphere control,' but the experiments demonstrate only Rabi oscillations (rotation about an axis with both x and z components), Ramsey interference (free precession about z), and spin echo sequences (combinations of x-rotations and z-free evolution). These are sufficient for universal single-qubit control in principle, but the authors do not show a generic rotation about a second transverse axis (e.g., y) or demonstrate arbitrary state preparation via quantum process tomography. The claim in the Discussion is stronger than what the data explicitly show. I recommend either softening the claim to 'control along multiple axes using standard pulse sequences' or adding an explicit demonstration of a rotation about the y-axis and a tomographic check of a non-trivial target state.","section":"Discussion, first paragraph"}],"minor_comments":[{"comment":"The definitions of γ and δγ are confusing: the text first states γ=(γ1+γ2)/2 and δγ=(γ1−γ2)/2, with γ1,2 presumably real loss rates, but then Eq. (3) contains factors iδγ and −i2πγ I. Please clarify the signs and whether δγ is intended to be real or imaginary; the sign convention for the σz term relative to Eq. (1) should be stated explicitly.","section":"Eq. (3) and surrounding text"},{"comment":"The caption of Fig. 1c does not specify the detuning values used for the Rabi oscillations; the text mentions Δ = ±20 Hz for the chiral trajectories but not for Fig. 1c. Please list the parameters in the caption.","section":"Fig. 1 caption"},{"comment":"The manuscript contains a typo: 'free procession' should be 'free precession' in the Ramsey section. Also, the abstract's claim of 'high-quality-factor electro-acoustic coupled cavities' is somewhat misleading because the effective quality factor is largely determined by the active feedback, rather than being a passive property of the cavities alone.","section":"Various"},{"comment":"The availability statement relies on 'available from the corresponding author upon request,' which is a weak form of data sharing. I encourage the authors to place the data and analysis scripts in a permanent repository to support reproducibility.","section":"Code and Data Availability"}],"recommendation":"major_revision","confidential_remarks":"The core concern about the feedback loop serving as both control and readout is serious and should be the primary focus of the revision. The paper's present form does not rule out that the observed 'Bloch dynamics' are simply the tracking response of the active loop. If the authors can supply a convincing independent readout calibration and error bars, the work would be a solid demonstration for a specialized applied-physics venue. I also note that the novelty is limited relative to prior classical two-level emulations (e.g., nanomechanical and photonic-crystal analogues), but the low-cost acoustic platform and the Floquet EP discussion give it a reasonable niche."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"You should know one thing up front: this paper does what it says—it shows Rabi oscillations, Ramsey fringes, a Floquet-enhanced lifetime, and spin echo rephasing in a pair of coupled electro-acoustic cavities at room temperature. The theory-experiment agreement in Figures 1–4 is visually convincing, and the central curves are direct solutions of the stated two-level Hamiltonian, not fits with free parameters. That is real work and worth taking seriously.\n\nWhat is actually new is the platform: a programmable, electrically driven acoustic two-level system that implements a full suite of single-qubit control primitives. Prior classical demonstrations used nanomechanical or photonic systems; doing it in low-cost stainless-steel cavities with commercial amplifiers and phase shifters is a practical step for education and acoustic field shaping. I buy that.\n\nWhere I get uneasy is the feedback architecture. The same active loops that set the loss parameters and coupling are also, as far as I can tell, the only readout of the mode amplitudes. The stress-test concern is fair: if the monitored signal is part of the control loop, then the observed trajectories may be the loop tracking its own setpoints rather than evidence for the intended Hamiltonian. The paper doesn't provide an open-loop calibration or an independent monitor to rule this out. I'd want that before accepting 'full Bloch-sphere control' as established. This is the weakest link.\n\nSecond, there are no error bars, no repeated-run statistics, and no quantitative fidelity or tomography. The word 'high-fidelity' appears, but nothing measures fidelity. That's a minor-to-moderate problem given the demonstrations are qualitative, but it matters for the stronger claims.\n\nThird, the long T1 and T2* are engineered by active feedback and Floquet driving. The paper mentions this, but it should be front and center: these are not intrinsic properties of the acoustic system. That is fine for classical emulation, but the framing currently risks overstatement.\n\nFinally, no code or raw data are released. 'Available upon request' is not reproducible science.\n\nOverall, I think the central physics is sound, the novelty is modest but real, and the biggest issues are about validation and transparency, not the core idea. This deserves a serious referee, but the authors should be asked for independent readout calibration, error bars, and a data release before publication.","headline":"A credible, reader-friendly classical emulator of single-qubit Bloch dynamics, but the active-feedback architecture and missing statistics leave the strongest claims under-supported.","tokens_in":9984,"tokens_out":1790,"would_cite":false,"duration_ms":23893,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Two acoustic cavities can reproduce full Bloch-sphere control of a quantum bit.","keywords":["acoustic two-level system","Bloch sphere dynamics","Rabi oscillations","Ramsey interferometry","spin echo","Floquet engineering","electro-acoustic cavities","coherent control"],"falsifier":"If the measured Ramsey fringe period did not scale as $1/\\Delta$ over the claimed range, or if the echo refocusing failed to return the state to $|0\\rangle$ for free-evolution times beyond those reported while the theory says it must, the reconstructed Hamiltonian would be shown to be wrong; a targeted test would drive with two different values of $\\Delta$ and check the interference null positions quantitatively against Eq. (1).","tokens_in":1556,"feed_emoji":"🔊","tokens_out":3136,"duration_ms":91274,"temperature":0.7,"pith_summary":"The paper shows that a pair of coupled, electrically driven acoustic cavities can act as a classical two-level system whose state is tracked on the Bloch sphere. By reprogramming the detuning, losses, and coupling on millisecond timescales, the authors implement Rabi oscillations, Floquet-driven dissipation suppression, Ramsey fringes, and spin-echo refocusing, with measured trajectories matching the two-level Schrödinger equation. The significance is that full coherent-control physics, normally associated with quantum bits, can be emulated in an inexpensive, room-temperature acoustic device, and the same control tools can be applied to precision sound-field shaping.","feed_headline":"Acoustic cavities perform full Bloch-sphere control at room temperature","feed_subtitle":"Rabi, Ramsey, and spin-echo protocols now run on low-cost electro-acoustic hardware with millisecond programming.","key_machinery":"The load-bearing object is the time-dependent two-level Hamiltonian $H(t)$ (as written in Eq. 1), with tunable detuning $\\Delta(t)$, loss rates $\\gamma_1(t)$ and $\\gamma_2(t)$, and coupling $\\kappa(t)$, together with the Schrödinger-type equation $i\\,d|\\psi\\rangle/dt = H_{\\mathrm{drive}}(t)|\\psi\\rangle$. Because the feedback network can switch these parameters with millisecond timing, the system can synthesize continuous, composite, and periodic drives, including the Floquet-modulated PT-symmetric part that lowers the gain threshold and extends coherence; this Hamiltonian is what maps every protocol onto a Bloch-sphere trajectory.","core_discovery":"The central claim is that complete Bloch-sphere dynamics can be realized classically: the complex amplitudes of two high-$Q$ acoustic cavity modes are made to obey the same Schrödinger-type equation as a driven qubit, with $\\Delta(t)$, $\\gamma_1(t)$, $\\gamma_2(t)$, and $\\kappa(t)$ actively modulated by feedback circuits. The experiment demonstrates each control primitive, including continuous driving yielding chiral Bloch trajectories, periodic Floquet switching of loss rates lowering the exceptional-point threshold and sustaining oscillations, Ramsey interference with $T_2^*\\approx 0.19$ s, and composite pulse sequences that refocus the state to a predetermined final point independent of free-evolution time. The stated result is full programmability of the state vector on the Bloch sphere, not just of its population.","pith_inferences":["Scaling the same electro-acoustic feedback architecture to arrays of cavities could emulate multi-level or lattice Hamiltonians, making acoustic analogues of topological bands and non-Abelian gauge fields experimentally accessible.","Because the hardware operates at ambient conditions and low cost, it could serve as an instructional platform for visualizing Bloch-sphere dynamics in undergraduate laboratories.","The demonstrated control could be pushed further with dynamical-decoupling sequences, potentially pushing the effective coherence time toward the $T_1$ limit and enabling more complex quantum-inspired protocols."],"forward_implications":["Rabi, Ramsey, and spin-echo sequences can now be programmed as software-defined control in an acoustic device, meaning the quantum-control toolkit transfers to sound-field engineering.","Floquet modulation of loss rates provides a practical route to extending state lifetime in classical two-level systems, with the exceptional-point threshold set jointly by coupling, loss imbalance, and modulation period.","The measured $T_2^*\\approx 0.19$ s gives an acoustic Ramsey-interferometry method for characterizing coherence and phase noise in coupled cavities.","Composite pulse sequences can be used for time-focused acoustic energy delivery, since the final field converges to the target state for a range of free-evolution durations."],"supporting_citations":[{"why":"Demonstrates nonadiabatic dynamics of two coupled nanomechanical resonator modes, supporting the two-mode coherent evolution picture.","marker":"[21]"},{"why":"Shows coherent control of a classical nanomechanical two-level system, the direct precursor of classical Bloch dynamics.","marker":"[22]"},{"why":"Establishes the concept of a strongly driven two-level system realized in a classical optical setting.","marker":"[24]"},{"why":"Demonstrates temporal adiabatic passage between detuned acoustic cavities, underpinning the electro-acoustic modulation platform.","marker":"[26]"},{"why":"Supplies the pulse-sequence framework and error analysis used for the composite pulse protocols.","marker":"[32]"},{"why":"Provides the Floquet exceptional-point threshold condition that the acoustic Floquet experiment tests.","marker":"[34]"},{"why":"Introduces the separated-oscillating-fields method that the Ramsey sequence is based on.","marker":"[37]"},{"why":"Introduces spin echoes, the refocusing protocol adapted in the acoustic composite pulse sequence.","marker":"[39]"}],"fun_headline_variants":["Acoustic cavities mimic qubit control on a budget","Full Bloch-sphere control on low-cost acoustic hardware","Classical acoustic qubit: full Bloch-sphere control","Low-cost acoustic system runs Rabi, Ramsey, and spin echo"],"cache_read_input_tokens":12160,"weakest_assumption_plain":"The whole reconstruction assumes the feedback circuits can independently and quickly tune the three Hamiltonian parameters without introducing uncontrolled phase shifts or amplitude-dependent distortion, and that the real-time monitoring used to track the state does not disturb the very dynamics it records.","fun_headline_variants_meta":{"raw":{"variants":["Acoustic cavities mimic qubit control on a budget","Full Bloch-sphere control on low-cost acoustic hardware","Classical acoustic qubit: full Bloch-sphere control","Low-cost acoustic system runs Rabi, Ramsey, and spin echo"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.00091,"raw_usage":{"total_tokens":3892,"prompt_tokens":906,"completion_tokens":2986,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":522,"completion_tokens_details":{"reasoning_tokens":2919}},"tokens_in":522,"tokens_out":2986,"duration_ms":22186,"temperature":1.0,"reasoning_tokens":2919,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T13:33:32.902382+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"If the measured Ramsey fringe period did not scale as $1/\\Delta$ over the claimed range, or if the echo refocusing failed to return the state to $|0\\rangle$ for free-evolution times beyond those reported while the theory says it must, the reconstructed Hamiltonian would be shown to be wrong; a targeted test would drive with two different values of $\\Delta$ and check the interference null positions quantitatively against Eq. (1).","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Demonstrates nonadiabatic dynamics of two coupled nanomechanical resonator modes, supporting the two-mode coherent evolution picture."},{"cited_title":"J., Kotthaus, J","cited_arxiv_id":null,"evidence_quote":"Shows coherent control of a classical nanomechanical two-level system, the direct precursor of classical Bloch dynamics."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Establishes the concept of a strongly driven two-level system realized in a classical optical setting."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Demonstrates temporal adiabatic passage between detuned acoustic cavities, underpinning the electro-acoustic modulation platform."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the Floquet exceptional-point threshold condition that the acoustic Floquet experiment tests."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Introduces the separated-oscillating-fields method that the Ramsey sequence is based on."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Introduces spin echoes, the refocusing protocol adapted in the acoustic composite pulse sequence."}],"review_version":1}