Periodic Reporting for period 4 - SiMS (Simulated Majorana states)
Berichtszeitraum: 2022-09-01 bis 2024-07-31
Topological protection provides a route to protect fragile quantum states, which are otherwise very sensitive to noise and thermal fluctuations of the environment that surrounds them. In 2010, it was theoretically proposed that such topological protection could be achieved in hybrid nanoscale devices consisting of superconductor and semiconductor layers. The resulting quantum states, owing to the similarities with the theory of Ettore Majorana from the 1930’s, are called Majorana modes. The experimental search for the Majorana modes has been fueled by the possibility to reach hardware quantum error correction, vital for scalable quantum computation and would eliminate the huge number of physical quantum bits required for an error corrected logical quantum bit needed in the case of other types of quantum hardware.
The goal of the project is to investigate a novel direction in the creation of Majorana states, which is based on a linear array of quantum dots with superconducting leads. The key advantage of this physical implementation is the control of the device parameters, which will allow us to reproducibly map the topological phase diagram of the system. In order to achieve this overarching goal, we will utilize low frequency as well as microwave domain measurement techniques and will build our devices using narrow gap III-V semiconductors together with conventional metallic superconductors. Furthermore, we will investigate the non-locality of the Majorana bound states, and in doing so, we will demonstrate superconducting molecular states spanning between neighboring quantum dots.
Our experimental progress in the field of topological state of matter, quantum computation methods and cryogenic technologies together substantiates the scientific and societal impact of the project. To strengthen this impact and to lower the access threshold of our results, we have adhered to the principles of open science and open hardware development throughout the project.
The goal of the project is to investigate a novel direction in the creation of Majorana states, which is based on a linear array of quantum dots with superconducting leads. The key advantage of this physical implementation is the control of the device parameters, which will allow us to reproducibly map the topological phase diagram of the system. In order to achieve this overarching goal, we will utilize low frequency as well as microwave domain measurement techniques and will build our devices using narrow gap III-V semiconductors together with conventional metallic superconductors. Furthermore, we will investigate the non-locality of the Majorana bound states, and in doing so, we will demonstrate superconducting molecular states spanning between neighboring quantum dots.
Our experimental progress in the field of topological state of matter, quantum computation methods and cryogenic technologies together substantiates the scientific and societal impact of the project. To strengthen this impact and to lower the access threshold of our results, we have adhered to the principles of open science and open hardware development throughout the project.
Throughout the first part of the project, we have demonstrated the first model system, a double quantum dot device with superconducting leads. We have showed that the charge- and spin-state control and readout by means of the supercurrent that flows through the device. This successful experiment opened the way for the longer quantum dot chains, which will form the nanodevice required to fulfill the final goals of the project.
In addition, we have also demonstrated that an on-chip refrigeration method can cool down nanoscale electronic devices to unprecedentedly low temperatures in the microkelvin regime. This achievement will be useful to reduce thermal fluctuations in upcoming measurements, and may facilitate more precise tuning of the underlying quantum states or allow for longer operation times.
The project successfully demonstrated all the necessary building blocks of topological superconductivity and its detection methods. We have developed a microwave resonator geometry tailored for bound state spectroscopy in semiconductor nanowires, in particular in large in-plane magnetic fields. We have showed that double-junction devices with non-local correlations can be embedded in this architecture as a vital element for quantum state manipulation and readout. Finally, given the emerging experimental and theoretical evidence of the relatively weak topological superconducting gap, we have showcased a nuclear refrigeration method for nanoelectronic devices.
Our results were disseminated in several peer reviewed scientific publications, invited and contributed talks on conferences as well as poster presentations by the research team. However, technological exploitation is beyond the scope of the current project owing to its low technological readiness level (TRL).
In addition, we have also demonstrated that an on-chip refrigeration method can cool down nanoscale electronic devices to unprecedentedly low temperatures in the microkelvin regime. This achievement will be useful to reduce thermal fluctuations in upcoming measurements, and may facilitate more precise tuning of the underlying quantum states or allow for longer operation times.
The project successfully demonstrated all the necessary building blocks of topological superconductivity and its detection methods. We have developed a microwave resonator geometry tailored for bound state spectroscopy in semiconductor nanowires, in particular in large in-plane magnetic fields. We have showed that double-junction devices with non-local correlations can be embedded in this architecture as a vital element for quantum state manipulation and readout. Finally, given the emerging experimental and theoretical evidence of the relatively weak topological superconducting gap, we have showcased a nuclear refrigeration method for nanoelectronic devices.
Our results were disseminated in several peer reviewed scientific publications, invited and contributed talks on conferences as well as poster presentations by the research team. However, technological exploitation is beyond the scope of the current project owing to its low technological readiness level (TRL).
During the project, we have demonstrated several technological advancements going beyond the state of the art, and list them grouped by the scientific field.
Cryogenic technologies: we have achieved a clear scientific breakthrough with a nanoscale electronic refrigeration technique breaking the millikelvin barrier for the first time. This is an enabling technology to improve quantum coherence of spins or superconducting devices in solid state devices.
Non-local electronic states in Kitaev chain devices: we have successfully demonstrated the presence of non-local correlations in both double quantum dot and three-terminal double-junction superconductor-semiconductor nanodevices, thus confirming the possibility of topological superconductivity in this system.
Measurement protocols of non-local quantum states: we have demonstrated both supercurrent spectroscopy and microwave spectroscopy as a viable tool to quantum state measurement in devices with non-local correlations. These experiments contribute to the field of quantum computation with topologically protected electronic states.
Cryogenic technologies: we have achieved a clear scientific breakthrough with a nanoscale electronic refrigeration technique breaking the millikelvin barrier for the first time. This is an enabling technology to improve quantum coherence of spins or superconducting devices in solid state devices.
Non-local electronic states in Kitaev chain devices: we have successfully demonstrated the presence of non-local correlations in both double quantum dot and three-terminal double-junction superconductor-semiconductor nanodevices, thus confirming the possibility of topological superconductivity in this system.
Measurement protocols of non-local quantum states: we have demonstrated both supercurrent spectroscopy and microwave spectroscopy as a viable tool to quantum state measurement in devices with non-local correlations. These experiments contribute to the field of quantum computation with topologically protected electronic states.