REVIEW
Anomalously Slow Cross Symmetry Phase Relaxation, Thermalized Non-Equilibrated Matter and Quantum Computing Beyond the Quantum Chaos Border
Quantum Physics · Submitted 27 Feb 2006 · 34 references
Pith's verdict: Interesting speculation, but the quantitative claim is undermined by a correlation amplitude that exceeds unity and by unexcluded non-compound photoproton emission; not ready for publication as is.
T0 · AI review
Why Pith says this
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Referee report
The paper
The paper claims
A thermalized quantum many-body system can retain phase memory of how it was formed for a time about eight orders of magnitude longer than thermalization itself.
The reading
What carries the argument
The central object is the cross-symmetry phase relaxation width $\beta$ introduced in Eq. (3): a parameter controlling the correlation between fluctuating S-matrix elements with different total spin and parity, $\langle S_{L_1}^* S_{L_2}\rangle = [\langle|S_{L_1}|^2\rangle\langle|S_{L_2}|^2\rangle]^{1/2}(1+\beta/\Gamma_{\mathrm{cn}})$. It is the inverse time over which the interference between states of different symmetry survives the energy averaging, i.e. the lifetime of the memory of the beam direction. Analysis of the Bi($\gamma$,p) angular distribution with this formula fixes $\beta/\Gamma_{\mathrm{cn}}=0.11$, and estimating $\Gamma_{\mathrm{cn}}\simeq 0.1$ eV from width systematics gives $\beta\simeq 0.01$ eV against $\Gamma_{\mathrm{spr}}\simeq 2$\textendash 4.5 MeV. This ratio is what carries the entire argument: without the tiny $\beta$, the angular asymmetry would vanish and the evaporating protons would be symmetric about 90 degrees.
Extended reading notes
Core claim
On the paper's own terms, the discovery is that complete energy thermalization in a compound nucleus does not imply the erasure of all phase information: the angular distribution of evaporating protons retains a forward-backward asymmetry that can only come from spin-parity off-diagonal correlations between S-matrix elements surviving energy averaging. The paper identifies the inverse lifetime of these correlations, the cross-symmetry phase relaxation width $\beta$, as the quantity that is anomalously small: $\beta \simeq 0.01$ eV against an estimated spreading width $\Gamma_{\mathrm{spr}} \simeq 2$\textendash 4.5 MeV. The resulting phase memory time $\tau_{\mathrm{ph}} = \hbar/\beta$ is about eight orders of magnitude longer than the thermalization time, so the compound nucleus behaves as a thermalized yet non-equilibrated many-body state. The same effect was previously seen in nucleon-induced reactions with a five-order separation; the electromagnetic entrance channel studied here is presented as a step closer to loading mechanisms in proposed quantum computers.
Load-bearing premise
The argument assumes that the entire measured forward-peaked angular distribution is compound-nucleus evaporation captured by the standard formula with one cross-symmetry parameter $\beta$; if direct, semi-direct, or pre-equilibrium photoproton emission contributes substantially to the forward peaking, the fitted $\beta$ would not measure phase relaxation and the eight-order separation collapses.
Editorial extensions
If this is right
- Energy thermalization and phase relaxation are separate clocks in highly excited many-body systems, and the phase clock can be slower by many orders of magnitude.
- A compound nucleus can serve as a physical demonstration that useful information about the loading channel survives for $\sim 6\times10^{-14}$ s, long after the $\sim 3\times10^{-22}$ s onset of quantum chaos.
- The analysis suggests that quantum computing protocols could in principle run on timescales set by $\hbar/\beta$, not $\hbar/\Gamma_{\mathrm{spr}}$, extending feasible qubit numbers toward $n\simeq 100$\textendash 1000.
- Because the entrance channel here is electromagnetic, the result is closer to the loading mechanisms envisioned for proposed quantum computers than the earlier nucleon-induced reactions.
- The effect is not limited to this reaction: the same formalism predicts non-vanishing spin-parity off-diagonal correlations in other strongly overlapping resonance reactions.
Reading between the lines
- Extending beyond the paper, a decisive microscopic derivation of $\beta$ \textendash{} currently stated to be an open problem \textendash{} would need to explain why interference between different spin-parity components survives energy averaging in a Hilbert space of effective dimension $\sim 10^{16}$.
- If the interpretation is right, the same $\beta$ should also appear in other electromagnetic entrance channels, such as $(\gamma,n)$ or electron-induced reactions, whose angular distributions could be checked against existing data.
- A testable extension would look for analogous long-lived directional memory in cold-atom or mesoscopic systems with strong interactions and large effective Hilbert spaces, transferring the nuclear finding to a controlled setting.
- The quantum-computing claim is illustrative rather than a device proposal: the load-bearing insight is that coherence lifetimes in dense interacting many-body systems are not bounded by the local thermalization time.
Original abstract
Thermalization in highly excited quantum many-body system does not necessarily mean a complete memory loss of the way the system was formed. This effect may pave a way for a quantum computing, with a large number of qubits $n\simeq 100$--1000, far beyond the quantum chaos border. One of the manifestations of such a thermalized non-equilibrated matter is revealed by a strong asymmetry around 90$^\circ $ c.m. of evaporating proton yield in the Bi($\gamma$,p) photonuclear reaction. The effect is described in terms of anomalously slow cross symmetry phase relaxation in highly excited quantum many-body systems with exponentially large Hilbert space dimensions. In the above reaction this phase relaxation is about eight orders of magnitude slower than energy relaxation (thermalization).
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
Thermalization in highly excited quantum many-body system does not necessarily mean a complete memory loss of the way the system was formed. This effect may pave a way for a quantum computing, with a large number of qubits $n\simeq 100$--1000, far beyond the quantum chaos border. One of the manifestations of such a thermalized non-equilibrated matter is revealed by a strong asymmetry around 90$^\circ $ c.m. of evaporating proton yield in the Bi($\gamma$,p) photonuclear reaction. The effect is described in terms of anomalously slow cross symmetry phase relaxation in highly excited quantum many-body systems with exponentially large Hilbert space dimensions. In the above reaction this phase relaxation is about eight orders of magnitude slower than energy relaxation (thermalization).
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Thermalization in highly excited quantum many-body system does not necessarily mean a complete memory loss of the way the system was formed. | background 0.58 | 0.17 | 0.51 | asserted 0.85 |
| s1 | This effect may pave a way for a quantum computing, with a large number of qubits $n\simeq 100$--1000, far beyond the quantum chaos border. | interpretation 0.96 | 0.21 | 0.39 | hedged possibility 1.00 |
| s2 | One of the manifestations of such a thermalized non-equilibrated matter is revealed by a strong asymmetry around 90$^\circ $ c.m. of evaporating proton yield in the Bi($\gamma$,p) photonuclear reaction. | result 0.96 | 0.66 | 0.12 | asserted 0.89 |
| s3 | The effect is described in terms of anomalously slow cross symmetry phase relaxation in highly excited quantum many-body systems with exponentially large Hilbert space dimensions. | interpretation 0.94 | 0.54 | 0.31 | asserted 0.99 |
| s4 | In the above reaction this phase relaxation is about eight orders of magnitude slower than energy relaxation (thermalization). | result 1.00 | 0.73 | 0.20 | asserted 1.00 |
What was examined, and what was not
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Figures
Figures reproduced from arXiv:quant-ph/0602224 by the authors.
References
How the literature uses it
1 arXiv paper cite this in 1 sentence
Discussion
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