Electronic noise—From advanced materials to quantum technologies Free

The science of electronic fluctuations and noise has been one of the most important branches of applied physics. The investigation of noise is essential for the understanding of physical processes in various materials and devices.^1–5 Various manifestations of electronic noise are commonly classified into four basic types, which include thermal noise, shot noise, generation–recombination noise, and low-frequency 1/f noise (f is the frequency). Two of these types, thermal and shot noise, have their origin in the random motion of charge carriers, and both have a spectral density that does not depend on frequency. The generation–recombination noise is observed at low frequencies, and its spectral density is described by the Lorentzians associated with the specific charge-trapping states. The low-frequency 1/f noise originates from different fluctuation processes, e.g., in the number of carriers or their mobility or both.^6–9 The importance of 1/f noise in electronics has motivated numerous studies on its physical mechanisms and the development of methods for its reduction. However, despite almost a century of research, the 1/f noise research field remains active, and numerous debates continue about its origin and mechanisms.^10,11

With downscaling of electrical devices, such as transistors, and sensors, 1/f noise starts to play an ever-growing role.^12,13 Individual traps in gate oxide gain more significance, and 1/f noise in transistors tends to grow inversely proportional to the device dimensions. Quantum dots with decreasing size become remarkably influenced by background charge fluctuations with strong implications for their applications, for example, as qubits. For these small devices, 1/f noise and shot noise measurements are indispensable in evaluating their technological applicability. Furthermore, non-equilibrium phenomena become important in small samples.^14,15 Lack of thermalization leads to randomness in quantized charge carriers. Consequently, even regular metallic conductors on the submicrometer scale at low temperatures display shot noise when the carriers are not able to thermalize to the environmental heat bath on short distances. This applies similarly to the micrometer-sized samples of the low-dimensional materials that are of great interest at present.¹⁶ Hence, shot noise investigations are powerful for studying dynamics in nano-scale devices under various pulsing and non-equilibrium conditions. In the limit of dominating shot noise, the sensitivity of a sensing device is bound by the so-called standard quantum limit, which dictates that the measurement sensitivity improves with the time as ∼1/t^0.5 (t is the time).¹⁷ The only way to surpass this limit is to utilize quantum resources, for example, entanglement. In the present-day quantum technology, there is a strong effort to employ entanglement for reaching the Heisenberg limit of scaling, which would allow sensitivity improvement as ∼1/t.¹⁸ The success of this scaling is related to the control of dephasing of quantum states, which may arise from back action noise from a measuring device, typically, either due to shot noise or 1/f noise.¹² These considerations explain the importance of continuing investigation of 1/f and shot noise in the context of new technologies.

Harnessing quantum coherence and entanglement is the key prerequisite for implementation of any quantum technological platform, be it quantum information processing, communication, or something else.^19,20 The efficiency of current quantum technologies based on coherent nanodevices is limited by material-inherent noise sources, frequently with 1/f-type spectrum.^13,19 The noise sources induce decoherence,^21,22 limiting the quantum evolution toward specific targets with fidelities sufficient for error correction codes. Fault-tolerant qubits with topological protection against local sources of noise have emerged as a possible alternative.^23,24 Quantum control methods aiming at limiting decoherence also lead to the possibility to reconstruct the frequency spectrum of fluctuations affecting coherent nanodevices, a task commonly referred to as noise spectroscopy, which, nowadays, also deals with higher-order spectral correlation functions.²⁵ While noise is often detrimental to the device's performance, it can reveal information about material quality, electronic transport, temperature, fractionally charged quasiparticles, or recombination and relaxation processes.^26–30 Noise spectroscopy approaches have become instrumental in the investigation of electronic transport in two-dimensional (2D) and one-dimensional (1D) charge-density-wave materials and devices.^31–34 It has been demonstrated that 1/f and generation–recombination noise can be used as a sensing parameter.^35–40 These applied physics discoveries and technological developments have opened up a new research area bridging together materials science, quantum device engineering, advanced quantum control, and, more recently, machine learning methods.⁴¹ 

The Special Issue on Electronic Noise—From Advanced Materials to Quantum Technologies presents reports on recent developments in experimental and theoretical aspects of electronic noise and fluctuation processes across a wide spectrum of scientific and technological fields. The topics covered in the Special Issue include thermal noise and shot noise in advanced materials and devices; low-frequency 1/f noise and generation–recombination noise in electronics; low-frequency 1/f noise in graphene and 2D materials; charge, flux, and critical current 1/f noise in superconducting systems; noise in semiconductors and in spin qubits; microscopic models for 1/f noise; decoherence in quantum devices due to 1/f noise; low-frequency noise spectroscopy as a reliability tool for electronics; noise in strongly correlated systems; low-frequency noise in magnonic and spintronic devices; noise spectroscopy as the material characterization tool; noise in microwave devices due to two-level systems; noise and correlations in quantum amplifiers; quantum squeezing of noise; measurement techniques beyond standard quantum limit; noise and entanglement in pumped systems; and low-frequency phase noise in spin Hall nano-oscillators.

A large number of papers describe noise in new material systems, such as ZrS₃ van der Waals semiconductor nanoribbons, IrO₂ Dirac nanowires, hafnia-based ferroelectric tunnel junctions, HZO ferroelectrics, Er³⁺ single-ion magnets, monolithic Al–Ge–Al nanowires, indium tin oxide transistor channels under stress, and fluoropolymer dielectric organic transistors.^42–49 A few papers report the noise studies specifically in ultra-wide-band-gap (UWBG) semiconductor devices based on AlGaN, β-(Al_xGa_1−x)₂O₃, and β-Ga₂O₃.^28,50,51 A group of papers in this Special Issue deals with low-frequency noise in metal–oxide–semiconductor transistors (MOSFETs), the correlations between noise and trap distribution in such devices, as well the effect of scaling on the noise in complementary metal–oxide semiconductor (CMOS) transistors.^52–55 The noise in graphene and other two-dimensional (2D) materials and devices continues to attract significant attention. Several papers in this Special Issue cover noise in 2D MoS₂, dual-gated graphene devices, 2D semi-Dirac material systems, graphene–Si Schottky barrier diodes, and suspended graphene.^56–60 

This Special Issue offers broad coverage of noise studies pertinent to the development of quantum device technologies, including noise in the semiconductor quantum dots, Josephson junctions, parametric oscillators, Bi₂Se₃ topological thin films, entangled electron systems, microwave resonators, spin Hall nano-oscillators, superconducting aluminum devices, neuromorphic computing, and silicon spin-qubits.^61–71 The theory developments, covered in this Special Issue, include simulation of noise in the ground state energy of electrons in gated quantum dots, theory of full counting statistics of ultrafast quantum transport, key exchanger, noise of topological insulators, thermal fluctuations in magnetic nanoparticle systems, non-Gaussian noise, second spectrum of fluctuations in graphene, noise–dissipation relation for nonlinear electronic circuits, and approaches for squeezing electronic noise.^72–80 

In conclusion, this Special Issue presents an exciting selection of new experimental and theoretical results associated with electronic noise, including noise in advanced materials, electronic and optoelectronic devices, and quantum technologies. We hope that this Special Issue will be stimulating for researchers, engineers, and students.

We thank all the authors who contributed to this Special Issue. Special thanks go to Professor Lesley F. Cohen, Editor-in-Chief, Dr. Jenny Stein, Journal Manager, and Jaimee-Ian Rodriguez, Editorial Assistant of Applied Physics Letters, for their help in the preparation of this Special Issue. A.A.B. acknowledges the support of the Vannevar Bush Faculty Fellowship from the Office of Secretary of Defense, under the Office of Naval Research Contract No. N00014-21-1-2947. P.J.H. is grateful to the Research Council of Finland, Grant No. 341913, EFT, and to the Ministry of Education and Culture in Finland, Aalto University's MEC Global Program. E.P. acknowledges the PNRR MUR Project PE0000023-NQSTI and COST Action CA 21144 Superqumap. Special thanks go to Dr. Subhajit Ghosh, UCLA, for useful discussions and help in manuscript preparation.

The authors have no conflicts to disclose.

Alexander A. Balandin: Conceptualization (lead). Elisabetta Paladino: Conceptualization (equal). Pertti J. Hakonen: Conceptualization (equal).

The data that support the findings of this study are available from the corresponding author upon reasonable request.