Slow Mixing of Quantum Gibbs Samplers

• URL: http://arxiv.org/abs/2411.04300v1
• Date: Wed, 06 Nov 2024 22:51:27 GMT
• Title: Slow Mixing of Quantum Gibbs Samplers
• Authors: David Gamarnik, Bobak T. Kiani, Alexander Zlokapa,
• Abstract summary: We present a quantum generalization of these tools through a generic bottleneck lemma. This lemma focuses on quantum measures of distance, analogous to the classical Hamming distance but rooted in uniquely quantum principles. Even with sublinear barriers, we use Feynman-Kac techniques to lift classical to quantum ones establishing tight lower bound $T_mathrmmix = 2Omega(nalpha)$.
• Score: 47.373245682678515
• License:
• Abstract: Preparing thermal (Gibbs) states is a common task in physics and computer science. Recent algorithms mimic cooling via system-bath coupling, where the cost is determined by mixing time, akin to classical Metropolis-like algorithms. However, few methods exist to demonstrate slow mixing in quantum systems, unlike the well-established classical tools for systems like the Ising model and constraint satisfaction problems. We present a quantum generalization of these tools through a generic bottleneck lemma that implies slow mixing in quantum systems. This lemma focuses on quantum measures of distance, analogous to the classical Hamming distance but rooted in uniquely quantum principles and quantified either through Bohr spectrum jumps or operator locality. Using our bottleneck lemma, we establish unconditional lower bounds on the mixing times of Gibbs samplers for several families of Hamiltonians at low temperatures. For classical Hamiltonians with mixing time lower bounds $T_\mathrm{mix} = 2^{\Omega(n^\alpha)}$, we prove that quantum Gibbs samplers also have $T_\mathrm{mix} = 2^{\Omega(n^\alpha)}$. This applies to models like random $K$-SAT instances and spin glasses. For stabilizer Hamiltonians, we provide a concise proof of exponential lower bounds $T_\mathrm{mix} = 2^{\Omega(n)}$ on mixing times of good $n$-qubit stabilizer codes at low constant temperature, improving upon previous bounds of $T_\mathrm{mix} = 2^{\Omega(\sqrt n)}$. Finally, for $H = H_0 + h\sum_i X_i$ with $H_0$ diagonal in $Z$ basis, we show that a linear free energy barrier in $H_0$ leads to $T_\mathrm{mix} = 2^{\Omega(n)}$ for local Gibbs samplers at low temperature and small $h$. Even with sublinear barriers, we use Poisson Feynman-Kac techniques to lift classical bottlenecks to quantum ones establishing an asymptotically tight lower bound $T_\mathrm{mix} = 2^{n^{1/2-o(1)}}$ for the 2D transverse field Ising model.

Related papers

• A polynomial-time dissipation-based quantum algorithm for solving the ground states of a class of classically hard Hamiltonians [4.500918096201963]
  We give a quantum algorithm for solving the ground states of a class of Hamiltonians. The mechanism of the exponential speedup that appeared in our algorithm comes from dissipation in open quantum systems.
  arXiv  Detail & Related papers  (2024-01-25T05:01:02Z)
• Time-Efficient Quantum Entropy Estimator via Samplizer [7.319050391449301]
  Estimating the entropy of a quantum state is a basic problem in quantum information. We introduce a time-efficient quantum approach to estimating the von Neumann entropy $S(rho)$ and R'enyi entropy $S_alpha(rho)$ of an $N$-dimensional quantum state $rho.
  arXiv  Detail & Related papers  (2024-01-18T12:50:20Z)
• Towards large-scale quantum optimization solvers with few qubits [59.63282173947468]
  We introduce a variational quantum solver for optimizations over $m=mathcalO(nk)$ binary variables using only $n$ qubits, with tunable $k>1$. We analytically prove that the specific qubit-efficient encoding brings in a super-polynomial mitigation of barren plateaus as a built-in feature.
  arXiv  Detail & Related papers  (2024-01-17T18:59:38Z)
• A Unified Framework for Uniform Signal Recovery in Nonlinear Generative Compressed Sensing [68.80803866919123]
  Under nonlinear measurements, most prior results are non-uniform, i.e., they hold with high probability for a fixed $mathbfx*$ rather than for all $mathbfx*$ simultaneously. Our framework accommodates GCS with 1-bit/uniformly quantized observations and single index models as canonical examples. We also develop a concentration inequality that produces tighter bounds for product processes whose index sets have low metric entropy.
  arXiv  Detail & Related papers  (2023-09-25T17:54:19Z)
• A lower bound on the space overhead of fault-tolerant quantum computation [51.723084600243716]
  The threshold theorem is a fundamental result in the theory of fault-tolerant quantum computation. We prove an exponential upper bound on the maximal length of fault-tolerant quantum computation with amplitude noise.
  arXiv  Detail & Related papers  (2022-01-31T22:19:49Z)
• On quantum algorithms for the Schr\"odinger equation in the semi-classical regime [27.175719898694073]
  We consider Schr"odinger's equation in the semi-classical regime. Such a Schr"odinger equation finds many applications, including in Born-Oppenheimer molecular dynamics and Ehrenfest dynamics.
  arXiv  Detail & Related papers  (2021-12-25T20:01:54Z)
• Improved spectral gaps for random quantum circuits: large local dimensions and all-to-all interactions [0.0]
  We show that $1D$ random quantum circuits have a spectral gap scaling as $Omega(n-1)$, provided that $t$ is small compared to the local dimension: $t2leq O(q)$. Our second result is an unconditional spectral gap bounded below by $Omega(n-1log-1(n) t-alpha(q))$ for random quantum circuits with all-to-all interactions.
  arXiv  Detail & Related papers  (2020-12-09T19:00:50Z)
• Quantum Algorithms for Simulating the Lattice Schwinger Model [63.18141027763459]
  We give scalable, explicit digital quantum algorithms to simulate the lattice Schwinger model in both NISQ and fault-tolerant settings. In lattice units, we find a Schwinger model on $N/2$ physical sites with coupling constant $x-1/2$ and electric field cutoff $x-1/2Lambda$. We estimate observables which we cost in both the NISQ and fault-tolerant settings by assuming a simple target observable---the mean pair density.
  arXiv  Detail & Related papers  (2020-02-25T19:18:36Z)
• Quantum Coupon Collector [62.58209964224025]
  We study how efficiently a $k$-element set $Ssubseteq[n]$ can be learned from a uniform superposition $|Srangle of its elements. We give tight bounds on the number of quantum samples needed for every $k$ and $n$, and we give efficient quantum learning algorithms.
  arXiv  Detail & Related papers  (2020-02-18T16:14:55Z)

This list is automatically generated from the titles and abstracts of the papers in this site.

This site does not guarantee the quality of this site (including all information) and is not responsible for any consequences.