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arXiv:2407.09631

Temperature limits of the transitional quantum dynamics in qubit clusters exposed to the ac field

Serhii Shafraniuk

Published Jul 12, 2024• 0 citations
arXivHTMLPDF

Abstract

Extending the temperature limits of quantum coherence in the system representing a chain of coupled two-level systems (TLS) exposed to an electromagnetic field is complicated due to the adverse influence of noise. Such a system frequently serves as a basic element of various quantum devices. In the steady state, the quantum coherence in TLS is merely destroyed by noise, which intensifies as the temperature increases. The behavior is complicated when the external field is applied modulating also the noise. In this work, using the computerized model, we study the temperature limits of the transitional quantum dynamics in the all-electrically controlled graphene single-TLS and three-TLS devices exposed to the electromagnetic field. We analyze how the external ac field changes the state of the system and observe that it not only influences the coherent transport there but modifies the effect of noise. The conducted numerical experiments determine the conditions provided the quantum coherence in QC may be much prolonged even above the ambient room temperature which can improve the performance of various quantum devices.

DOI
10.48550/arxiv.2407.09631

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Extending the temperature limits of quantum coherence in the system representing a chain of coupled two-level systems (TLS) exposed to an electromagnetic field is complicated due to the adverse influence of noise. Such a system frequently serves as a basic element of various quantum devices. In the steady state, the quantum coherence in TLS is merely destroyed by noise, which intensifies as the temperature increases. The behavior is complicated when the external field is applied modulating also the noise. In this work, using the computerized model, we study the temperature limits of the transitional quantum dynamics in the all-electrically controlled graphene single-TLS and three-TLS devices exposed to the electromagnetic field. We analyze how the external ac field changes the state of the system and observe that it not only influences the coherent transport there but modifies the effect of noise. The conducted numerical experiments determine the conditions provided the quantum coherence in QC may be much prolonged even above the ambient room temperature which can improve the performance of various quantum devices.
Abstract Graphene, with its two-dimensional carbon structure, exhibits unique quantum properties that are crucial for quantum computing. In this paper, we investigate the influence of an external electromagnetic field on quantum coherence and entanglement between two qubits in graphene lattices. Our findings show that an electromagnetic field with high field strength (ξ 0 ∼ 50 meV2) and low frequency (ω = 0.117 eV) significantly enhances quantum entanglement and coherence, even at elevated temperatures (T ∼ 20 meV). By adjusting the frequency and the field strength, these quantum effects can be preserved long enough at high temperatures. Furthermore, circular polarization of the electromagnetic field is found to be more effective than linear and elliptical polarizations in optimizing these effects. These results highlight the critical role of electromagnetic fields in enhancing quantum properties, potentially paving the way for advancements in quantum computing and related technologies.
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Two-level systems (TLSs) are the major source of dephasing of spin qubits in numerous quantum computing platforms. In spite of much effort, it has been difficult to substantially mitigate the effects of this noise or, in many cases, to fully understand its physical origin. We propose a method to make progress on both of these issues. When an oscillating field is applied to a TLS, stochastic resonance can occur and the noise spectrum is moved to higher frequencies. This shift in the TLS noise spectrum will increase the dephasing times of the qubits that they influence. Furthermore, the details of this effect depend on the physical properties of the noise sources. Thus one can use qubit spectroscopy to investigate their physical properties, specifically the extent to which the TLSs themselves possess quantum coherence. We find that it should be possible to determine the dephasing rate and the energy-level separation of the TLS themselves in this way.
Two-level systems (TLS) are the major source of dephasing of spin qubits in numerous quantum computing platforms. In spite of much effort, it has been difficult to substantially mitigate the effects of this noise or, in many cases, to fully understand its physical origin. We propose a method to make progress on both of these issues. When an oscillating field is applied to a TLS, stochastic resonance can occur and the noise spectrum is moved to higher frequencies. This shift in the TLS noise spectrum will increase the dephasing times of the qubits that they influence. Furthermore, the details of this effect depend on the physical properties of the noise sources. Thus one can use qubit spectroscopy to investigate their physical properties, specifically the extent to which the TLS themselves possess quantum coherence. We find that it should be possible to determine the dephasing rate and the energy level separation of the TLS themselves in this way.
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The efficiency of the future devices for quantum information processing is limited mostly by the finite decoherence rates of the individual qubits and quantum gates. Recently, substantial progress was achieved in enhancing the time within which a solid-state qubit demonstrates coherent dynamics. This progress is based mostly on a successful isolation of the qubits from external decoherence sources obtained by engineering. Under these conditions, the material-inherent sources of noise start to play a crucial role. In most cases, quantum devices are affected by noise decreasing with frequency fff approximately as 1/f1/f1/f. According to the present point of view, such noise is due to material- and device-specific microscopic degrees of freedom interacting with quantum variables of the nanodevice. The simplest picture is that the environment that destroys the phase coherence of the device can be thought of as a system of two-state fluctuators, which experience random hops between their states. If the hopping times are distributed in an exponentially broad domain, the resulting fluctuations have a spectrum close to 1/f1/f1/f in a large frequency range. This paper reviews the current state of the theory of decoherence due to degrees of freedom producing 1/f1/f1/f noise. Basic mechanisms of such noises in various nanodevices are discussed and several models describing the interaction of the noise sources with quantum devices are reviewed. The main focus of the review is to analyze how the 1/f1/f1/f noise destroys their coherent operation. The start is from individual qubits concentrating mostly on the devices based on superconductor circuits and then some special issues related to more complicated architectures are discussed. Finally, several strategies for minimizing the noise-induced decoherence are considered.