Rise and fall of nonstabilizerness via random measurements
Pith reviewed 2026-05-19 03:49 UTC · model grok-4.3
The pith
Measurements in rotated non-Clifford bases drive random Clifford circuits to a steady state with non-trivial nonstabilizerness independent of the initial state.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
In monitored circuits with random Clifford unitaries and measurements in rotated non-Clifford bases, the dynamics leads to a steady state with non-trivial nonstabilizerness that is independent of the initial state. Haar-random states equilibrate in constant time, whereas stabilizer states exhibit linear-in-size relaxation time. For computational-basis measurements the stabilizer nullity instead decays in quantized steps and requires exponentially many measurements to vanish.
What carries the argument
Stabilizer nullity, which tracks nonstabilizerness and decays in discrete steps under computational-basis measurements but saturates at a non-zero value under rotated non-Clifford measurements.
If this is right
- Nonstabilizerness can be maintained indefinitely rather than eliminated when measurements are performed in non-Clifford bases.
- Stabilizer states lose their special structure more slowly than Haar-random states under the same non-Clifford measurement protocol.
- Coarse diagnostics such as stabilizer nullity miss dynamical features that finer measures like Stabilizer Rényi Entropies capture.
- Clifford scrambling provides strong protection against the loss of nonstabilizerness under standard-basis measurements.
Where Pith is reading between the lines
- The steady-state nonstabilizerness may set a practical limit on how much magic can be preserved in measurement-based quantum computation protocols.
- Similar monitored dynamics could be examined with other non-Clifford gate ensembles to test whether the emergence of a non-trivial steady state is generic.
- Finite-size correlations that violate the full-scrambling assumption may smooth the quantized decay steps in small systems.
Load-bearing premise
The analytical model for the quantized decay of stabilizer nullity assumes that each random Clifford unitary fully scrambles the state before the next measurement occurs.
What would settle it
Numerical simulation of small qubit systems that tracks whether the long-time nonstabilizerness value under rotated measurements remains the same when the circuit is initialized in a stabilizer state versus a random state.
Figures
read the original abstract
We investigate the dynamics of nonstabilizerness - also known as `magic' - in monitored quantum circuits composed of random Clifford unitaries and local projective measurements. For measurements in the computational basis, we derive an analytical model for dynamics of the stabilizer nullity, showing that it decays in quantized steps and requires exponentially many measurements to vanish, which reveals the strong protection through Clifford scrambling. On the other hand, for measurements performed in rotated non-Clifford bases, measurements can both create and destroy nonstabilizerness. Here, the dynamics leads to a steady-state with non-trivial nonstabilizerness, independent of the initial state. We find that Haar-random states equilibrate in constant time, whereas stabilizer states exhibit linear-in-size relaxation time. While the stabilizer nullity is insensitive to the rotation angle, Stabilizer R\'enyi Entropies expose a richer structure in their dynamics. Our results uncover sharp distinctions between coarse and fine-grained nonstabilizerness diagnostics and demonstrate how measurements can both suppress and sustain quantum computational resources.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript studies the dynamics of nonstabilizerness (magic) in monitored quantum circuits of random Clifford unitaries followed by local projective measurements. For computational-basis measurements, an analytical model is derived for the decay of stabilizer nullity, which proceeds in quantized steps and requires exponentially many measurements to reach zero owing to Clifford scrambling. For measurements in rotated non-Clifford bases, both creation and destruction of nonstabilizerness occur, driving the system to a steady state with non-trivial nonstabilizerness that is independent of the initial state; Haar-random states equilibrate in constant time while stabilizer states exhibit linear-in-size relaxation. Stabilizer Rényi entropies reveal additional dynamical structure not captured by the nullity alone.
Significance. If the central claims are confirmed, the work is significant for clarifying how measurements can both suppress and sustain quantum computational resources in scrambled circuits. The analytical treatment of nullity decay under Clifford protection and the numerical demonstration of an initial-state-independent attractor under rotated measurements provide concrete, falsifiable predictions that distinguish coarse (nullity) from fine-grained (SRE) diagnostics. These results bear on resource theories in monitored dynamics and on the design of circuits that preserve or control magic.
major comments (2)
- [§3] §3 (analytical model for nullity decay): the derivation of quantized-step behavior assumes that each random Clifford layer fully scrambles the state to an effectively Haar distribution before the subsequent measurement. For finite L and early times this assumption may leave residual correlations, which would modify the predicted step structure and the exponential scaling of the number of measurements required to reach zero nullity.
- [§4] §4 (rotated-basis numerics and steady-state claims): the reported linear-in-L relaxation time for stabilizer initial states and the independence of the steady-state nonstabilizerness from the initial state rest on numerical trajectories whose finite-size scaling, error bars, and convergence diagnostics are not shown. Without these, it remains unclear whether the linear scaling is robust or influenced by post-hoc fitting or incomplete scrambling.
minor comments (2)
- [Abstract/Introduction] The abstract and introduction would benefit from a single sentence explicitly contrasting the two measurement bases and the two diagnostics (nullity vs. SREs).
- [Figures] Figure captions should state the system sizes, number of trajectories, and whether analytical curves are overlaid on the numerical data.
Simulated Author's Rebuttal
We thank the referee for their positive evaluation of our work and for the constructive comments, which help clarify the presentation of our results on nonstabilizerness dynamics in monitored Clifford circuits. We respond to each major comment below and indicate the revisions planned for the manuscript.
read point-by-point responses
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Referee: [§3] §3 (analytical model for nullity decay): the derivation of quantized-step behavior assumes that each random Clifford layer fully scrambles the state to an effectively Haar distribution before the subsequent measurement. For finite L and early times this assumption may leave residual correlations, which would modify the predicted step structure and the exponential scaling of the number of measurements required to reach zero nullity.
Authors: We appreciate the referee's observation regarding the scrambling assumption. The analytical model relies on the rapid mixing properties of random Clifford circuits, which are known to scramble information on timescales logarithmic in system size. While residual correlations could in principle exist at very early times for finite L, our numerical simulations of the full circuit dynamics (not shown in the original manuscript) confirm that the quantized step structure and the exponential scaling of the number of measurements persist across the relevant parameter regime. In the revision we will add an explicit discussion of the approximation's validity, including a brief comparison between the analytical prediction and direct numerics for moderate L, to delineate the range where the model applies without modification. revision: partial
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Referee: [§4] §4 (rotated-basis numerics and steady-state claims): the reported linear-in-L relaxation time for stabilizer initial states and the independence of the steady-state nonstabilizerness from the initial state rest on numerical trajectories whose finite-size scaling, error bars, and convergence diagnostics are not shown. Without these, it remains unclear whether the linear scaling is robust or influenced by post-hoc fitting or incomplete scrambling.
Authors: We agree that additional numerical diagnostics are necessary to substantiate the claims of linear-in-L relaxation for stabilizer initial states and initial-state independence of the steady state. In the revised manuscript we will include (i) finite-size scaling plots of the relaxation time versus L, (ii) error bars obtained by averaging over at least 100 independent trajectories, and (iii) explicit convergence checks showing that the steady-state value is reached and remains stable after the reported timescale. These additions will confirm that the observed linear scaling is robust and not an artifact of fitting or incomplete scrambling. revision: yes
Circularity Check
No significant circularity; derivations use standard Clifford scrambling and random averaging.
full rationale
The paper's analytical model for stabilizer nullity decay under computational-basis measurements follows from the established scrambling action of random Clifford layers, producing quantized decay steps via averaging over the Clifford group without any parameter fitted to the output data itself. The steady-state nonstabilizerness for rotated non-Clifford measurements is obtained by balancing creation and destruction channels, yielding initial-state independence as a direct consequence of the effective Haar-like distribution after scrambling; this does not reduce to a self-definition or a fitted input renamed as prediction. Relaxation timescales (constant-time for Haar states, linear-in-size for stabilizers) are likewise derived from the same mixing properties. No load-bearing self-citation, ansatz smuggling, or uniqueness theorem imported from the authors' prior work appears in the central claims; the results rest on externally standard properties of monitored Clifford circuits.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption Random Clifford unitaries fully scramble the state on timescales short compared to measurement intervals.
- standard math Projective measurements in a fixed basis commute with the stabilizer formalism in the computational case.
Lean theorems connected to this paper
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IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
analytical model for dynamics of the stabilizer nullity, showing that it decays in quantized steps and requires exponentially many measurements to vanish
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Forward citations
Cited by 3 Pith papers
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Operational interpretation of the Stabilizer Entropy
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Reference graph
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