1/f Noise from Condensed Matter Physics to Quantum Technologies

Apr 24, 2022, 8:00 AM → Apr 30, 2022, 10:00 PM Europe/Rome

Ettore Majorana Foundation and Centre for Scientific Culture

The Course is organized within the EMFCSC International School of Nonequilibrium Phenomena  directed by Alessandra Lanzara, Massimo G. Palma and Bernardo Spagnolo. The aim of the Course is to give a broad overview of the current understanding of the phenomenon of 1/f noise in condensed matter physics, with emphasis on its role in nanodevices for quantum information processing, quantum communications, and material science. The School targets the audience of young researchers such as Ph.D. students and post-docs.  Lectures will be given by renowned experimental and theoretical physicists and engineers working on 1/f noise both from material science and quantum computing perspectives. During lectures, the most recent advances will be put in the framework of the current understanding of a phenomenon that has a long tradition of studies. Young participants from around the world will be exposed to cutting-edge research topics and the newest methodologies in the EMFCSC friendly atmosphere, reaping benefit in terms of enthusiasm, knowledge, and new ideas.

News. Julian Schwinger foundation best poster awards: Prizes for the two best posters will be awarded to young researchers (Ph.D. and young post-docs) attending school. The winners will be announced during the social dinner.

List of Topics

• 1/f noise in metals 
• Low-frequency 1/f noise in graphene and other 2D materials and devices 
• Charge, flux, and critical current 1/f noise in superconducting qubits 
• 1/f noise in semiconductors, 2DEG, and semiconductor charge and spin qubits 
• Microscopic models for 1/f noise in superconducting devices
• Microscopic tunneling systems
• Fluctuating electric dipoles and magnetic moments in superconducting circuits
• Decoherence due to 1/f noise
• Approaches to non-Markovian open quantum systems
• Quantum sensing via dynamical decoupling
• Low-frequency noise spectroscopy as a reliability tool for electronics
• Low-frequency noise in charge-density-wave materials and other strongly correlated systems
• Low-frequency noise in magnonic and spintronic devices

Course Directors 

A.A. Balandin
Y. Galperin
P. Hakonen
E. Paladino
A. Ustinov

 

Organizing Committee

E. Paladino
F.M.D. Pellegrino
L. Giannelli

 

       

POSTER_ONEOVERF2022.pdf

Sunday, April 24

3:00 PM → 8:00 PM Arrival and Registration

Monday, April 25

8:45 AM → 9:00 AM Directors: Opening - E. Paladino

9:00 AM → 11:00 AM A. Balandin: Low-frequency 1/f noise in graphene and other 2D materials and devices

Abstract:
In this lecture, I will start with an introduction consisting of a brief historical overview and the fundamental properties of the 1/f noise in metals and semiconductors. The introduction will include basic information on the noise mechanisms and sources – fluctuations in the number of carriers vs. fluctuations of the mobility, surface vs. volume effects, and approaches for studying the noise in electronic devices. In the second part of the lecture, I will describe the characteristics of 1/f noise in graphene and other quasi-two-dimensional (2D) materials and devices. Graphene and few-layer graphene constitute a convenient material platform for addressing some of the fundamental questions of the 1/f noise research field. On the other side, reduction of 1/f noise is a requirement for any practical application of 2D materials in communications or sensors [1]. The topics of discussion will include the effect of defects, introduced in a controllable way, on the 1/f noise level [2], and the use of the low-frequency noise as a signal in sensors based on graphene field-effect transistors [3]. In the third part of the lecture, I will focus on low-frequency noise in quasi-2D charge-density-wave (CDW) materials and devices. A CDW phase is a macroscopic quantum state consisting of a periodic modulation of the electronic charge density accompanied by a periodic distortion of the atomic. The CDW field experiences rebirth owing to the emergence of quasi-2D and 1D layered van der Waals materials that reveal numerous CDW phases, including some that exist above the room temperature [4-5]. I will describe the “narrow-band noise” in 2D materials, the sliding of CDWs in 1T-TaS2, and the use of low-frequency noise for monitoring the phase transitions and CDW depinning in 2D CDW quantum materials.

[1] A. A. Balandin, Nature Nano, 8, 549 (2013); [2] M. Z. Hossain, et al., Appl. Phys. Lett., 102, 153512 (2013); [3] S. Rumyantsev, et al., Nano Lett., 12, 2294 (2012); [4] G. Liu, et al., Nature Nano, 11 845 (2016); [5] A. A. Balandin, S. V. Zaitzev-Zotov, and G. Grüner, Appl. Phys. Lett., 119, 170401 (2021); [6] A. Mohammadzadeh, et al., Appl. Phys. Lett., 118, 223101 (2021).

11:00 AM → 11:30 AM Coffee Break

11:30 AM → 1:30 PM Clare Yu: 1/f Flux Noise in Superconducting Qubits

Abstract:
The superconducting Josephson junction is one of the leading candidates for making a qubit. A major obstacle to the realization of quantum computers with Josephson junction qubits is noise and decoherence of the wavefunction. We will discuss various sources of noise. We then focus on one of the major types of noise, called flux noise, which is due to fluctuating magnetic spins on the surface of metals.
We will describe our work on the microscopic sources of this flux noise; namely oxygen molecules adsorbed on the surface as well as atomic hydrogen. If time permits, we will also discuss puzzles such as the value of the noise exponent and pivoting of noise spectra.

1:30 PM → 3:00 PM Lunch

3:00 PM → 4:00 PM S. Kubaktin: Sources of Decoherence In Superconducting Quantum Devices

Abstract:
Quantum information technology puts stringent demands on the quality of materials and interfaces in the pursuit of increased device coherence. Yet, little is known about the chemical structure and origins of paramagnetic impurities that produce flux/charge noise causing decoherence of fragile quantum states and impeding the progress towards large- scale quantum computing. Our on-chip electron-spin resonance techniques [1] gave vital clues to the long-standing problem of noise and decoherence in superconducting devices: a technique for on-chip Electron Spin Resonance allowed to identify, for the first time, the chemical species responsible for the flux noise in superconducting circuits [2,3]. Furthermore, the most recent noise measurements in superconducting resonators point to the link between charge and flux noise in superconducting circuits: a mild sample treatment has led to tenfold reduction of the surface spins, responsible for the flux noise, as evidenced by ESR, and this treatment has also led to tenfold reduction of the low frequency noise in superconducting resonator, associated with the charge noise [4]. We have developed tunable resonators [5] to evaluate the density of states of decohering defects. Our results demonstrate a previously unexplored decoherence mechanism in the form of a new type of TLS originating from trapped QPs, which can induce qubit relaxation [6]. By extending our tunable resonator techniques, we have got an access to microscopic Hamiltonians of interacting TLF [7] – the incoherent low-energy fluctuators which have been previously only postulated in theory. Furthermore, to get more insight on g=2 spins, reported in [3], we have applied a high magnetic-field electron paramagnetic resonance (HFEPR) and hyperfine multi-spin spectroscopy on α-Al2O3, a common substrate for quantum devices (an amorphous Al2O3 is also unavoidably present in aluminum-based superconducting circuits and qubits). The identified paramagnetic centers are immanent to the surface and have a well-defined but highly complex structure that extends over multiple hydrogen, aluminum and oxygen atoms. Modelling reveals that the radicals likely originate from well-known reactive oxygen chemistry common to many metal oxides. The chemical identification of the possible sources of noise in superconducting devices allows for an active chemical intervention, aiming at silencing the defects and, therefore, improving the coherence in superconducting quantum devices [8].

[1] Journ. of Appl. Phys. 112, 123905, (2012)
[2] Phys. Rev. Lett. 118, 057703, (2017)
[3] Phys. Rev. Lett. 118, 057702, (2017)
[4] Nature Comms. 9, 1143, (2018)
[5] Phys. Rev. Appl. 14, 044040, (2020)
[6] Sci. Adv. 6, (2020) DOI: 10.1126/sciadv.abc5055
[7] Phys. Rev. B 103, 174103, (2021)
[8] Sci. Adv. 8, (2022) DOI: 10.1126/sciadv.abm6169

4:00 PM → 5:00 PM L. Faoro: Challenges to the implementations of superconducting qubits posed by microscopic phenomena inherent to superconducting films

Abstract:
The implementation of surface code error correction in transmons-based superconducting qubits poses a formidable challenge, because, despite all the improvements of the last years, it seems that we remain dominated by Two Level Systems (TLS) (and correlated noise) that are intrinsic to superconductor. The main purpose of this mini course is to illustrate what we understand about the microscopic origin of noise in superconducting qubits and what are the challenges we need to overcome in order to achieve surface code error correction in large arrays of superconducting qubits. The lessons are structured to convey the physical picture [i.e, not many formulas].
Lesson I:
Review on our understanding of microscopic mechanism of noise in superconducting qubits (transmons) and superconducting resonators.
- Theory of non-conventional TLS and importance of TLS-TLS interaction.
- 1/f noise in resonators.
- 1/f charge noise in transmons vs 1/f charge noise in charge qubits and Single Electron Transistors.
- Interplay between spin and charge noise.

5:00 PM → 5:30 PM Coffee Break

5:30 PM → 6:30 PM S. Rumyanstev: 1/f noise of electrons and magnons

Abstract:
Although the history of the noise research goes back almost a century, the answers to even fundamental questions are still being discussed. We will review the history and main properties of the 1/f noise in semiconductors, metals, and graphene. We will discuss what causes the1/f fluctuations in these materials and how to compare the noise amplitude in different devices and materials.
It is proved that 1/f noise is caused by the resistance fluctuations. However, the fundamental question of the mobility versus number of carriers fluctuations is still being debated. We will review several proves that the 1/f noise in semiconductors is due to the fluctuations in the number of the charge carriers and look for the materials which might demonstrate the 1/f mobility fluctuations. One of the best candidates for such a material is graphene.
It was shown a while ago that measurements of noise under the condition of geometrical magnetoresistance allow to directly assess the mechanism of low-frequency fluctuations. This kind of experiment already proved that in the majority of cases the 1/f noise in semiconductors is due to the number of carriers fluctuations.
Recent measurements of noise in h-BN encapsulated graphene transistor under the condition of geometrical magnetoresistance prove that the mobility fluctuations are the dominant mechanism of the low frequency noise in high-quality graphene.
The second part of the talk is devoted to the low frequency noise of magnons, which are quanta of the electron spin wave in a crystal lattice. They can be used for information processing, sensing, and other applications. The magnonic device is a rare example of an electronic device based on the electrical insulator.
We will review the experimental results, which show that contrary to the majority of electronic devices the 1/f noise is not found yet in the magnonic devices. The low-frequency noise of magnonic devices is dominated by the generation recombination-like noise with the Lorentzian spectrum and by random telegraph signal noise, in many cases. The presence of the random telegraph signal noise is an indication that just one individual fluctuator causes the noise in a big device with millimeters characteristic dimensions. This is a striking difference with electronic devices where the random telegraph signal noise is usually found in submicron devices.
To conclude, the noise mechanisms are different in different materials and devices, and exaggerating the situation a bit, we can say that there are as many noise mechanisms as there are different electronic systems.

Tuesday, April 26

9:00 AM → 11:00 AM J. Koch: 1/f noise and other noise channels in superconducting qubits: modeling and simulation

Abstract:
Superconducting qubits currently rank high among the quantum hardware platforms that aspire to realize, ultimately, error-corrected quantum processors much larger than the ones available to date. A critical aspect, both historically as well as for the future roadmap of these devices, is the question of coherence times: for how long does a superconducting circuit faithfully represent quantum information stored in it, and what fidelities can we reach when performing gate operations on individual or pairs of qubits? This set of lectures will provide an introduction to the world of superconducting qubits from the perspective of modeling and simulation. Material to be covered includes the theoretical description of superconducting qubits like the transmon and fluxonium, the analysis of noise channels including 1/f charge and flux noise, and a hands-on tutorial to quantitative analysis of spectral properties and noise characteristics using the Python package "scqubits".
Participants are encouraged to install "scqubits" on their laptop prior to the lectures, see https://scqubits.readthedocs. for instructions.

Participants are encouraged to install "scqubits" on their laptop prior to Prof J. Koch's lectures (click here)

11:00 AM → 11:30 AM Coffee Break

11:30 AM → 1:30 PM J. Bylander: Loss and noise in superconducting quantum circuits: materials, device designs, quantum computing

Abstract:
In these lectures I will discuss the loss and noise that lead to decoherence of quantum processors. I will focus on the effect of microscopic noise processes, how we can do experiments to learn about them, and how we can fabricate the materials and design the devices to be less sensitive to them. I will give examples from experiments with the point of view of someone developing superconducting quantum processor hardware.

1:30 PM → 3:00 PM Lunch

3:00 PM → 4:00 PM A. Balandin: Low-frequency 1/f noise in graphene and other 2D materials and devices

Abstract:
In this lecture, I will start with an introduction consisting of a brief historical overview and the fundamental properties of the 1/f noise in metals and semiconductors. The introduction will include basic information on the noise mechanisms and sources – fluctuations in the number of carriers vs. fluctuations of the mobility, surface vs. volume effects, and approaches for studying the noise in electronic devices. In the second part of the lecture, I will describe the characteristics of 1/f noise in graphene and other quasi-two-dimensional (2D) materials and devices. Graphene and few-layer graphene constitute a convenient material platform for addressing some of the fundamental questions of the 1/f noise research field. On the other side, reduction of 1/f noise is a requirement for any practical application of 2D materials in communications or sensors [1]. The topics of discussion will include the effect of defects, introduced in a controllable way, on the 1/f noise level [2], and the use of the low-frequency noise as a signal in sensors based on graphene field-effect transistors [3]. In the third part of the lecture, I will focus on low-frequency noise in quasi-2D charge-density-wave (CDW) materials and devices. A CDW phase is a macroscopic quantum state consisting of a periodic modulation of the electronic charge density accompanied by a periodic distortion of the atomic. The CDW field experiences rebirth owing to the emergence of quasi-2D and 1D layered van der Waals materials that reveal numerous CDW phases, including some that exist above the room temperature [4-5]. I will describe the “narrow-band noise” in 2D materials, the sliding of CDWs in 1T-TaS2, and the use of low-frequency noise for monitoring the phase transitions and CDW depinning in 2D CDW quantum materials.

[1] A. A. Balandin, Nature Nano, 8, 549 (2013); [2] M. Z. Hossain, et al., Appl. Phys. Lett., 102, 153512 (2013); [3] S. Rumyantsev, et al., Nano Lett., 12, 2294 (2012); [4] G. Liu, et al., Nature Nano, 11 845 (2016); [5] A. A. Balandin, S. V. Zaitzev-Zotov, and G. Grüner, Appl. Phys. Lett., 119, 170401 (2021); [6] A. Mohammadzadeh, et al., Appl. Phys. Lett., 118, 223101 (2021).

4:00 PM → 5:00 PM Clare Yu: 1/f Flux Noise in Superconducting Qubits

Abstract:
The superconducting Josephson junction is one of the leading candidates for making a qubit. A major obstacle to the realization of quantum computers with Josephson junction qubits is noise and decoherence of the wavefunction. We will discuss various sources of noise. We then focus on one of the major types of noise, called flux noise, which is due to fluctuating magnetic spins on the surface of metals.
We will describe our work on the microscopic sources of this flux noise; namely oxygen molecules adsorbed on the surface as well as atomic hydrogen. If time permits, we will also discuss puzzles such as the value of the noise exponent and pivoting of noise spectra.

5:00 PM → 5:30 PM Coffee Break

5:30 PM → 8:00 PM Poster Session

Wednesday, April 27

9:00 AM → 11:00 AM P. Hakonen: Electrical transport and limits of 1/f noise in suspended graphene

Abstract:
In these lectures, I will start by a brief review on fundamental transport phenomena in 2D materials, with the aim to outline the basic noise processes involved. I will give a brief overview of experimental results on graphene and MoS2 and discuss how their low-frequency noise spectra can be analyzed. Graphene and MoS2 can be viewed as archetype materials for 1/f noise phenomena in 2D semimetals and 2D semiconductors, respectively, and the presented concepts can be carried over to other equivalent materials. Furthermore, I will review results on suspended graphene devices which provide the lowest 1/f noise. Due to the low noise, suspended graphene provides a good test bed for studies of intrinsic and extrinsic noise sources, which facilitates fundamental tests of 1/f noise theories. Finally, 1/f noise in topological materials and in superconductor-graphene-superconductor junctions with proximity-induced supercurrent will be discussed.

11:00 AM → 11:30 AM Coffee Break

11:30 AM → 1:30 PM J. Bergli: Decoherence due to 1/f noise

Abstract:
We will consider the simple model of an ensemble of classical random telegraph processes which allows one to study the decoherence of a quantum system in cases where the environment dynamics is slow compared to the decoherence timescale. 1/f noise is one typical such noise source as it is dominated by low frequencies. We will mostly consider the case of pure dephasing, showing in detail how one can derive the decay of the quantum state in this model. We will also discuss the conditions under which the model is realistic and where it can fail.

1:30 PM → 3:00 PM Lunch

3:00 PM → 4:00 PM J. Koch: 1/f noise and other noise channels in superconducting qubits: modeling and simulation

Abstract:
Superconducting qubits currently rank high among the quantum hardware platforms that aspire to realize, ultimately, error-corrected quantum processors much larger than the ones available to date. A critical aspect, both historically as well as for the future roadmap of these devices, is the question of coherence times: for how long does a superconducting circuit faithfully represent quantum information stored in it, and what fidelities can we reach when performing gate operations on individual or pairs of qubits? This set of lectures will provide an introduction to the world of superconducting qubits from the perspective of modeling and simulation. Material to be covered includes the theoretical description of superconducting qubits like the transmon and fluxonium, the analysis of noise channels including 1/f charge and flux noise, and a hands-on tutorial to quantitative analysis of spectral properties and noise characteristics using the Python package "scqubits".
Participants are encouraged to install "scqubits" on their laptop prior to the lectures, see https://scqubits.readthedocs. for instructions.

Participants are encouraged to install "scqubits" on their laptop prior to Prof J. Koch's lectures (click here)

4:00 PM → 5:00 PM J. Bylander: Loss and noise in superconducting quantum circuits: materials, device designs, quantum computing

Abstract:
In these lectures I will discuss the loss and noise that lead to decoherence of quantum processors. I will focus on the effect of microscopic noise processes, how we can do experiments to learn about them, and how we can fabricate the materials and design the devices to be less sensitive to them. I will give examples from experiments with the point of view of someone developing superconducting quantum processor hardware.

5:00 PM → 5:30 PM Coffee Break

5:30 PM → 6:30 PM L. Faoro: Challenges to the implementations of superconducting qubits posed by microscopic phenomena inherent to superconducting films

Abstract:
The implementation of surface code error correction in transmons-based superconducting qubits poses a formidable challenge, because, despite all the improvements of the last years, it seems that we remain dominated by Two Level Systems (TLS) (and correlated noise) that are intrinsic to superconductor. The main purpose of this mini course is to illustrate what we understand about the microscopic origin of noise in superconducting qubits and what are the challenges we need to overcome in order to achieve surface code error correction in large arrays of superconducting qubits. The lessons are structured to convey the physical picture [i.e, not many formulas].
Lesson II:
Challenge to surface code error correction in large superconducting transmons arrays.
- Introduction to Google Sycamore and challenge to surface code error correction
- Evidence of highly correlated noise [both spatially and temporal (long-lasting)]
- TLS frequency drifts and problem with qubits calibrations.

Thursday, April 28

8:30 AM → 10:25 AM A. Ustinov: Identifying Material Defects in Superconducting Quantum Circuits

Abstract:
Material defects are currently recognized to be the main source of decoherence in superconducting
circuits employed for modern quantum computers. In structurally disordered solids, atoms or groups of
atoms are able to quantum mechanically tunnel between two nearly equivalent sites. These atomic
tunnelling systems have been previously identified as the cause of various low-temperature anomalies of
bulk glasses and as a source of decoherence of quantum circuits where they are sparsely present in the
disordered oxide barriers and on the surfaces of superconducting thin films. A tiny mechanical
deformation of the oxide barrier changes the energies of the atomic tunnelling systems. These changes
can be extracted from the microwave spectra of superconducting qubits and resonators. Tuning the
properties of individual defects by applying mechanical strain and/or external electrical fields allow to
study spectral properties, intrinsic relaxation and dephasing times, and detect mutual interactions between
defects. Progress towards reliable large-scale quantum processors requires prevention of defects by
improvements in device fabrication. On the other hand, quantum circuits also provide a novel and
effective method for studying the physics of defects and origins of noise which limit their operation.

10:25 AM → 10:40 AM Coffee Break

10:40 AM → 12:35 PM M. Friesen: A review of electrically gated quantum-dot qubits and related noise sources

Abstract:
Electrically gated quantum-dot qubits in group-IV semiconductors are widely studied in both academic and industrial settings, and are considered one of the leading prospects for large-scale quantum computing applications. In this review, I will described the operation of both charge and spin-based qubits and the noise sources that affect them. Topics will touch upon materials science, simple theoretical models, fundamental noise sources, and noise-mitigation strategies.

12:35 PM → 1:30 PM P. Hakonen: Electrical transport and limits of 1/f noise in suspended graphene

Abstract:
In these lectures, I will start by a brief review on fundamental transport phenomena in 2D materials, with the aim to outline the basic noise processes involved. I will give a brief overview of experimental results on graphene and MoS2 and discuss how their low-frequency noise spectra can be analyzed. Graphene and MoS2 can be viewed as archetype materials for 1/f noise phenomena in 2D semimetals and 2D semiconductors, respectively, and the presented concepts can be carried over to other equivalent materials. Furthermore, I will review results on suspended graphene devices which provide the lowest 1/f noise. Due to the low noise, suspended graphene provides a good test bed for studies of intrinsic and extrinsic noise sources, which facilitates fundamental tests of 1/f noise theories. Finally, 1/f noise in topological materials and in superconductor-graphene-superconductor junctions with proximity-induced supercurrent will be discussed.

1:30 PM → 2:30 PM Lunch

2:30 PM → 10:30 PM Excursion&Social Dinner

Friday, April 29

9:00 AM → 11:00 AM C. Enss: Dynamics of Low-energy Excitations in Disordered Non-equilibrium Quantum Systems

Abstract:
Amorphous solids are prototypes of disordered non-equilibrium quantum systems. At low
temperatures, the physics of such glassy materials is governed by atomic tunneling systems
and their interaction with other degrees of freedom such as phonons, nuclear moments, or
conduction electrons. The detailed understanding of such systems is not only of general
interest from a fundamental point of view, but also has implications for many novel applications
such as solid-state qubits, nanomechanical oscillators, or superconducting amplifiers
operating at the quantum limit, where atomic tunneling systems are a source of dissipation,
decoherence, and 1/f noise. We will give a general introduction to the physics of atomic
tunneling systems in disordered solids, focusing on dissipative processes, low-frequency
noise, and recent insights into the role of nuclear spin.

11:00 AM → 11:30 AM Coffee Break

11:30 AM → 1:00 PM G. Falci: Decoherence and quantum control in mutlilevel artificial atoms

1:00 PM → 1:30 PM F. Pellegrino: 1/f critical current noise in short ballistic graphene Josephson junctions

1:30 PM → 3:00 PM Lunch

3:00 PM → 4:00 PM M. Friesen: A review of electrically gated quantum-dot qubits and related noise sources

Abstract:
Electrically gated quantum-dot qubits in group-IV semiconductors are widely studied in both academic and industrial settings, and are considered one of the leading prospects for large-scale quantum computing applications. In this review, I will described the operation of both charge and spin-based qubits and the noise sources that affect them. Topics will touch upon materials science, simple theoretical models, fundamental noise sources, and noise-mitigation strategies.

4:00 PM → 5:00 PM A. Ustinov: Identifying Material Defects in Superconducting Quantum Circuits

Abstract:
Material defects are currently recognized to be the main source of decoherence in superconducting
circuits employed for modern quantum computers. In structurally disordered solids, atoms or groups of
atoms are able to quantum mechanically tunnel between two nearly equivalent sites. These atomic
tunnelling systems have been previously identified as the cause of various low-temperature anomalies of
bulk glasses and as a source of decoherence of quantum circuits where they are sparsely present in the
disordered oxide barriers and on the surfaces of superconducting thin films. A tiny mechanical
deformation of the oxide barrier changes the energies of the atomic tunnelling systems. These changes
can be extracted from the microwave spectra of superconducting qubits and resonators. Tuning the
properties of individual defects by applying mechanical strain and/or external electrical fields allow to
study spectral properties, intrinsic relaxation and dephasing times, and detect mutual interactions between
defects. Progress towards reliable large-scale quantum processors requires prevention of defects by
improvements in device fabrication. On the other hand, quantum circuits also provide a novel and
effective method for studying the physics of defects and origins of noise which limit their operation.

5:00 PM → 5:30 PM Coffee Break

5:30 PM → 6:30 PM Directors: Closing