1/f noise: implications for solid-state quantum information (1304.7925v2)

Abstract: The efficiency of the future devices for quantum information processing will be 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 clever 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, f, approximately as 1/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 a exponentially broad domain, the resulting fluctuations have a spectrum close to 1/f in a large frequency range. In this paper we review the current state of the theory of decoherence due to degrees of freedom producing 1/f noise. We discuss basic mechanisms of such noises in various nanodevices and then review several models describing the interaction of the noise sources with quantum devices. The main focus of the review is to analyze how the 1/f noise destroys their coherent operation. We start from individual qubits concentrating mostly on the devices based on superconductor circuits, and then discuss some special issues related to more complicated architectures. Finally, we consider several strategies for minimizing the noise-induced decoherence.

• The paper demonstrates that 1/f noise critically limits qubit coherence by inducing phase disruptions through microscopic interactions.
• The paper employs spin-fluctuator and semi-classical models to quantitatively assess decoherence in superconducting circuits.
• The paper outlines mitigation strategies, including dynamical decoupling and optimal point operations, to improve quantum gate performance.

Overview of "1/f Noise: Implications for Solid-State Quantum Information"

The paper "1/f Noise: Implications for Solid-State Quantum Information" addresses a critical component of solid-state quantum computing: the impact of 1/f noise on qubits and quantum gates. This noise, characterized by its frequency-dependent spectral density decreasing as 1/f, is pervasive in quantum devices and poses a major challenge in achieving high coherence times crucial for quantum information processing.

Key Concepts and Challenges

1/f noise, often arising from material-specific microscopic interactions, disrupts the phase coherence of quantum systems. The paper reviews the fundamental mechanisms behind 1/f noise, emphasizing its influence on superconducting circuits. These circuits are subject to various noise sources, including charge, flux, and critical current noise. The noise is typically modeled using two-state fluctuators, contributing to decoherence via random switching processes that can range over a wide spectrum of relaxation rates.

Impact on Quantum Coherent Operations

The inherent fluctuations of 1/f noise limit the coherent operation of solid-state qubits. The paper dives deep into superconducting systems, where the interplay between charge and flux influences the efficiency of quantum gates. Superconducting qubits, including charge, flux, and phase qubits, showcase diverse sensitivity to external noise, necessitating sophisticated methods to isolate and mitigate these effects.

Methodologies for Understanding and Mitigating 1/f Noise

The paper extensively employs theoretical models to describe the decoherence processes associated with 1/f noise. It highlights the current state of theoretical tools used to tackle these noise sources, such as spin-fluctuator models and semi-classical approaches for single and coupled qubit systems. These methodologies are pivotal in understanding how 1/f noise affects quantum coherence and in crafting strategies to minimize their impact.

Theoretical and Practical Implications

The implications of this research stretch into both theoretical explorations and practical applications in quantum computing. The review suggests that qubit performance heavily relies on detailed noise characterization and engineering of device architectures. Passive strategies like optimal point operation, along with active error correction techniques such as dynamical decoupling, are explored as means to enhance coherence times.

Future Directions

Acknowledging that the fight against 1/f noise is far from straightforward, the paper posits several future research directions. Developing materials with reduced inherent noise and crafting novel qubit designs that inherently resist decoherence are crucial. Additionally, the exploration of non-Gaussian noise models and their impact on qubit dynamics presents a frontier in improving quantum gate fidelities.

In essence, achieving scalable and reliable quantum computing requires overcoming the constraints imposed by 1/f noise, and this paper lays a robust foundation in understanding these challenges while pointing toward promising avenues for ongoing research and development.