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arXiv:2308.15836 · Physics Letters B

Position dependence of Nielsen complexity for the thermofield double state

Fatemeh Khorasani, Reza Pirmoradian, Mohammad Reza Tanhayi

Published Mar 19, 2024• 4 citations
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Abstract

In this paper, the Nielsen geometric method is used to study the position dependence of the Nielsen complexity for the thermofield double state of a harmonic oscillator. We present the state shift under the influence of an external electric field and demonstrate its importance for the construction of the corresponding circuit. By numerical analysis, we investigate the effect of the frequency and the external field on the dynamics of complexity. Our observation reveals that the system's complexity diminishes considerably with the rise of the frequency. Furthermore, our findings indicate that the complexity exhibits a distinct behavior under a feeble external electric field, as it grows more intricate with the escalation of the frequency. However, with higher magnitudes of the electric field, the system reverts to its prior behavior. We also remark on the influence of the reference state's frequency on the complexity.

DOI
10.1016/j.physletb.2024.138585

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In this paper, the Nielsen geometric method is used to study the position dependence of the Nielsen complexity for the thermofield double state of a harmonic oscillator. We present the state shift under the influence of an external electric field and demonstrate its importance for the construction of the corresponding circuit. By numerical analysis, we investigate the effect of the frequency and the external field on the dynamics of complexity. Our observation reveals that the system's complexity diminishes considerably with the rise of the frequency. Furthermore, our findings indicate that the complexity exhibits a distinct behavior under a feeble external electric field, as it grows more intricate with the escalation of the frequency. However, with higher magnitudes of the electric field, the system reverts to its prior behavior. We also remark on the influence of the reference state's frequency on the complexity.
In this paper, we investigate the circuit complexity of a quantum harmonic oscillator subjected to an external magnetic field. Utilizing the Nielsen approach within the thermofield dynamics (TFD) framework, we determine the complexity of thermofield double states as functions of time, temperature, and the external magnetic field. Our subsequent analysis reveals various features of this complexity. For instance, as temperature increases, the amplitude of complexity oscillations also rises, while at low temperatures, complexity stabilizes at a constant positive value. Furthermore, the magnetic field creates two distinct sectors: strong magnetic fields exhibit periodic complexity oscillations, whereas weak magnetic fields induce a beating effect. Finally, we confirm that the rate of complexity obeys the Lloyd bound.
Abstract We establish a systematic framework for studying quantum computational complexity of Gaussian states of charged systems based on Nielsen’s geometric approach. We use this framework to examine the effect of a chemical potential on the dynamics of complexity. As an example, we consider the complexity of a charged thermofield double state constructed from two free massive complex scalar fields in the presence of a chemical potential. We show that this state factorizes between positively and negatively charged modes and demonstrate that this fact can be used to relate it, for each momentum mode separately, to two uncharged thermofield double states with shifted temperatures and times. We evaluate the complexity of formation for the charged thermofield double state, both numerically and in certain analytic expansions. We further present numerical results for the time dependence of complexity. We compare various aspects of these results to those obtained in holography for charged black holes.
In this paper, we investigate the circuit complexity of a quantum charged particle in an external magnetic field. Utilizing the Nielsen approach, we determine the complexity of thermofield double states as functions of time, temperature, and cyclotron frequency. We analyze both the complexity and the amplitude of its oscillations across various parameter values, and reveal that these results cannot be derived as a limit of the harmonic oscillator case. Finally, we calculate the rate of complexity and show that it obeys the Lloyd bound.
Motivated by recent developments in studying the complexity of thermofield double states and the holographic complexity proposals in charged black hole backgrounds, here we use Nielsen's geometric approach to examine the complexity of the simple model of a charged thermofield double state constructed from two free complex scalar fields. We show that this state factorizes between positively and negatively charged modes and demonstrate that this can be used to translate the problem into that of two uncharged thermofield double states with shifted temperatures and times. We evaluate the complexity of formation for the charged thermofield double, both numerically and in certain analytic expansions, and present numerical results for the time dependence of complexity. We compare various aspects of these results to those obtained in holography for charged black holes.
Motivated by the holographic complexity proposals, in this paper, we investigate the time dependence of the complexity for the fermionic thermofield double state (TFD) using the Nielsen approach and Fubini-Study (FS) approach separately. In both two approaches, we discuss the results for different reference states: the Dirac vacuum state and the Gaussian state which has no spatial entanglement (NSE). For Dirac vacuum reference state, we find that the complexity by both two approaches is time independent and the circuit complexity shares the same expression for both methods with the L2{L}^{2}L2 norm. For the NSE reference state, the complexity by the Nielsen approach is time-dependent while it by the FS approach is time-independent. Further, we find our dynamical results are in good agreement with the bosonic case, where the complexity evolves in time and saturates after a time at the order of the inverse temperature. And we show that the complexity of formation is also shared same similar behaviors with the holographic complexity.
In this paper, we study circuit complexity in Proca theory with Nielsen's approach and Fubini-Study (FS) metric approach. We place the fields on a lattice to gain a regularized theory, and obtain the ground state by adopting proper coordinates. We calculate complexities of the ground and the thermofield double (TFD) states with Nielsen's approach---complexity of the TFD state is found to grow like a logarithmic function. We quantize the Proca fields and give the approximate ground state and the TFD state by applying unitary circuit operators to the associated reference states. The circuit lengths are calculated with a FS metric---the minimal lengths are given according to the associated geometric spaces. The complexity of the TFD state is found to grow linearly with time.