Quantum Causal Inference with Extremely Light Touch

• URL: http://arxiv.org/abs/2303.10544v3
• Date: Thu, 28 Mar 2024 07:32:35 GMT
• Title: Quantum Causal Inference with Extremely Light Touch
• Authors: Xiangjing Liu, Yixian Qiu, Oscar Dahlsten, Vlatko Vedral,
• Abstract summary: We give an explicit quantum causal inference scheme using quantum observations alone. We derive a closed-form expression for the space-time pseudo-density matrix associated with many times and qubits. We prove that if there is no signalling between two subsystems, the associated reduced state of the pseudo-density matrix cannot have negativity.
• Score: 0.0
• License: http://creativecommons.org/licenses/by-nc-sa/4.0/
• Abstract: We consider the quantum version of inferring the causal relation between events. There has been recent progress towards identifying minimal interventions and observations needed. We here give an explicit quantum causal inference scheme using quantum observations alone for the case of a bipartite quantum system with measurements at two times. In this scenario there may be combinations of temporal and spatial correlations. We derive a closed-form expression for the space-time pseudo-density matrix associated with many times and qubits. This matrix can be determined by coarse-grained quantum observations alone and the protocol is in that sense extremely light touch. We prove that if there is no signalling between two subsystems, the associated reduced state of the pseudo-density matrix cannot have negativity, regardless of the possible presence of initial spatial correlations. We further exploit the time asymmetry of the pseudo-density matrix to determine the temporal order of events. The negativity and time asymmetry are used to determine compatibility with 5 causal structures distinguished by the direction of causal influence and whether there are initial correlations or not. The protocol succeeds for a state with coherence undergoing a fully decohering channel, showing that coherence in the channel is not necessary for the quantum advantage of causal inference from observations alone.

Related papers

• Measuring the Evolution of Entanglement in Compton Scattering [101.11630543545151]
  The behavior of quantum entanglement during scattering is identical to the behavior of initially classically correlated photons up to a constant factor equal to two. Our dedicated experiment with photons confirms these results and explains the "Puzzle of Decoherence" observed recently.
  arXiv  Detail & Related papers  (2024-06-20T14:21:23Z)
• Operator representation of spatiotemporal quantum correlations [0.0]
  We prove that there does not exist an operator representation for general quantum correlations across space and time. In the case of qutrit systems, we use our results to illustrate an intriguing connection between light-touch observables and symmetric, informationally complete, positive operator-valued measures.
  arXiv  Detail & Related papers  (2024-05-27T18:00:02Z)
• Tracing quantum correlations back to collective interferences [0.04096453902709291]
  We investigate nonclassical correlations between two quantum systems in terms of quantum interferences between collective states of the two systems. We show that the relation between probability currents and correlations can be represented by continuous conditional (quasi)probability currents through the interferometer. Our results help to explain the meaning of nonlocal correlations in quantum mechanics, and support Feynman's claim that interference is the origin of all quantum phenomena.
  arXiv  Detail & Related papers  (2024-01-30T06:15:53Z)
• Real-time dynamics of false vacuum decay [49.1574468325115]
  We investigate false vacuum decay of a relativistic scalar field in the metastable minimum of an asymmetric double-well potential. We employ the non-perturbative framework of the two-particle irreducible (2PI) quantum effective action at next-to-leading order in a large-N expansion.
  arXiv  Detail & Related papers  (2023-10-06T12:44:48Z)
• Causal classification of spatiotemporal quantum correlations [0.0]
  We show that certain quantum correlations possess an intrinsic arrow of time, and enable classification of general quantum correlations across space-time. Our results indicate that certain quantum correlations possess an intrinsic arrow of time, and enable classification of general quantum correlations across space-time based on their (in)compatibility with various underlying causal structures.
  arXiv  Detail & Related papers  (2023-06-15T17:59:18Z)
• Observing super-quantum correlations across the exceptional point in a single, two-level trapped ion [48.7576911714538]
  In two-level quantum systems - qubits - unitary dynamics theoretically limit these quantum correlations to $2qrt2$ or 1.5 respectively. Here, using a dissipative, trapped $40$Ca$+$ ion governed by a two-level, non-Hermitian Hamiltonian, we observe correlation values up to 1.703(4) for the Leggett-Garg parameter $K_3$. These excesses occur across the exceptional point of the parity-time symmetric Hamiltonian responsible for the qubit's non-unitary, coherent dynamics.
  arXiv  Detail & Related papers  (2023-04-24T19:44:41Z)
• Bell inequalities with overlapping measurements [52.81011822909395]
  We study Bell inequalities where measurements of different parties can have overlap. This allows to accommodate problems in quantum information. The scenarios considered show an interesting behaviour with respect to Hilbert space dimension, overlap, and symmetry.
  arXiv  Detail & Related papers  (2023-03-03T18:11:05Z)
• From no-signalling to quantum states [0.0]
  Characterising quantum correlations from physical principles is a central problem in the field of quantum information theory. We suggest a natural generalisation of no-signalling in the form of no-disturbance to dilated systems.
  arXiv  Detail & Related papers  (2022-04-25T07:06:17Z)
• Quantum causal correlations and non-Markovianity of quantum evolution [0.0]
  A non-Markovianity measure for quantum channels is introduced based on causality measure. Breakdown of monotonicity of the causality measure is associated with the revival of temporal correlations.
  arXiv  Detail & Related papers  (2020-05-08T16:10:55Z)
• Entropic Uncertainty Relations and the Quantum-to-Classical transition [77.34726150561087]
  We aim to shed some light on the quantum-to-classical transition as seen through the analysis of uncertainty relations. We employ entropic uncertainty relations to show that it is only by the inclusion of imprecision in our model of macroscopic measurements that we can prepare a system with two simultaneously well-defined quantities.
  arXiv  Detail & Related papers  (2020-03-04T14:01:17Z)
• Interference of Clocks: A Quantum Twin Paradox [39.645665748998816]
  Phase of matter waves depends on proper time and is susceptible to special-relativistic (kinematic) and gravitational (redshift) time dilation. It is conceivable that atom interferometers measure general-relativistic time-dilation effects. We show that closed light-pulse interferometers without clock transitions during the pulse sequence are not sensitive to gravitational time dilation in a linear potential.
  arXiv  Detail & Related papers  (2019-05-22T12:30:57Z)

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.