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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

A scanning quantum cryogenic atom microscope at 6 K

The Scanning Quantum Cryogenic Atom Microscope (SQCRAMscope) is a quantum sensor in which a quasi-1D quantum gas images electromagnetic fields emitted from a nearby sample. We report improvements to the microscope. Cryogen usage is reduced by replacing the liquid cryostat with a closed-cycle system and modified cold finger, and cryogenic cooling is enhanced by adding a radiation shield. The minimum accessible sample temperature is reduced from 35~K to 5.7~K while maintaining low sample vibrations. A new sample mount is easier to exchange, and quantum gas preparation is streamlined.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

NECQST: Novel Electronics for Cryogenic Quantum Sensors Technology

Development of low-noise cryogenic readout circuits for SNSPDs based on state-of-the art, commercially available SiGe HBT technology, operating at a range of 1-4 Kelvin. Targeting a reduction of the timing jitter of SNSPDs (from the current record of 2.7 ps FWHM at 400 nm), and a reduction in the power dissipation allowed by the development of dedicated low-noise cryogenic amplifiers, which will enable the scaling of ultra-low-jitter SNSPDs to large arrays. Such performance advances will directly benefit the Caltech/Fermilab INQNET (Intelligent Quantum Networks & Technologies) program, which aims to demonstrate high-rate quantum communication at Fermilab.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Development of Quantum Computing Interconnect Based on Aerosol Jet Printing and Electrochemical Deposition of Rhenium

The electrodeposition of rhenium on to a metal seed layer on flexible substrates is presented as a means to creating superconducting flexible cable connectors in an enabling plug-and-play approach for quantum computing. Cryogenic quantum electronics are currently connected using masses of stainless-steel coaxial cables that are bulky, rigid - both in form and design - and lead to significant joule heating, thermal noise, and cross talk. Here, we present an unprecedented approach to integrate an aerosol jet printed (AJP) metal seed layer with rhenium electrodeposition on a flexible substrate in the advancement of superconducting interconnect technologies. Silver and gold were printed using the ‘Nanojet’ aerosol jet printer on Kapton films. Adhesion of gold was found to be far superior to that of silver and adhesion on roughened Kapton surpassed that of its smooth counterpart. Electrodeposition of rhenium was successful on both silver and gold and an amorphous Re film was confirmed by XRD. Results for both materials are presented however due to the poor adhesion of silver to Kapton it was ruled out as a viable candidate. Composite materials were characterized by profilometry, EDS, XRD and FIBSEM. Electrical measurements of the composite at ambient temperature showed a critical temperature (T c ), where the resistance drops to 0, of 5.8 K, well above 4.2 K, the temperature of liquid helium. Stress-strain tests of the Ag-Re and Au-Re composites on roughened and smooth Kapton were completed. Cyclic flexure testing (200 cycles) to 1.25% strain showed smooth Kapton samples reach a stress of ~16 MPa, while Kapton roughened with sandpaper, reaches ~20MPa of stress for the same 1.25% strain.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Better Than Worst-Case Decoding for Quantum Error Correction

The overheads of classical decoding for quantum error correction in cryogenic quantum systems grow rapidly with the number of logical qubits and their correction code distance. Decoding at room temperature is bottlenecked by refrigerator I/O bandwidth while cryogenic on-chip decoding is limited by area/power/thermal budget. To overcome these overheads, we are motivated by the observation that in the common case (over 90% of the time), error correction 'syndromes' are fairly trivial with high redundancy / sparsity, since the error correction codes are over-provisioned to be able to correct for uncommon worst-case complex scenarios (to ensure substantially low logical error rates). If suitably exploited, these trivial scenarios can be handled with insignificant overhead, thereby alleviating any bottlenecks towards handling the worst-case scenarios by state-of-the-art means. Here, we propose Better Than Worst-Case Decoding for Quantum Error Correction, targeting cryogenic quantum systems and Surface Code, consisting of: On-chip Clique Decoder: An extremely lightweight decoder for correcting trivial common-case errors, designed for the cryogenic domain. The decoder is implemented and evaluated for SFQ logic. Statistical Off-chip Bandwidth Allocation: A statistical confidence-based technique for allocation of off-chip decoding bandwidth, to efficiently handle the rare complex decodes that are not covered by the Clique Decoder. Decode-Overflow Execution Stalling: A method to stall circuit execution, for the worst-case scenarios in which the provisioned off-chip bandwidth is insufficient to complete all requested off-chip decodes. In all, BTWC decoding achieves 70-99+% off-chip bandwidth elimination across a range of logical and physical error rates, without significantly sacrificing the accuracy of a state-of-the-art off-chip decoder. Further, it achieves 10-1000x bandwidth reduction over prior bandwidth reduction techniques, as well as 15-37x resource overhead reduction compared to prior on-chip decoding.

cryogenic optimization↗
DOE OSTI2019

Towards Quantum-Limited Cryogenic Amplification for Multi-Qubit Platforms

Here we present the development of the building blocks of a Josephson parametric amplifier (JPA), namely the superconducting quantum interference device (SQUID) and the inductive pick-up coil that permits current coupling from a quantum dot into the SQUID. We also discuss our efforts in making depletion mode quantum dots using delta doped GaAs quantum wells. Because quantum dot based spin qubits utilize very low-level (~10 - 100pA), short duration (1ms - 1μs) current signals for state preparation and readout, these systems require close proximity cryogenic amplification to prevent signal corruption. Common amplification methods in these semiconductor quantum dots rely on heterojunction bipolar transistors (HBTs) and high electron mobility transistors (HEMTs) to amplify the readout signal from a single qubit. The state of the art for HBTs and HEMTs produce approximately 10µW of power when operating at high bandwidths. For few-qubit systems this level of heat dissipation is acceptable. However, for scaling up the number of qubits to several hundred or a thousand, the heat load produced in a 1 to 1 amplifier to qubit arrangement would overload the cooling capacity of a common dilution refrigerator, which typically has a cooling power of ~100µW at its base temperature. Josephson parametric amplifiers have been shown to dissipate ~1pW of power with current sensitivies on par with HBTs and HEMTs and with bandwidths 30 times that of HBTs and HEMTs, making them attractive for multi-qubit platforms. In this report we describe in detail the fabrication process flow for developing inductive pick-up coils and the fabrication and measurement of NbTiN and A1/A1Ox/A1 SQUIDs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Nematic transitions in iron pnictide superconductors imaged with a quantum gas

The Scanning Quantum Cryogenic Atom Microscope (SQCRAMscope) uses an atomic Bose–Einstein condensate to measure magnetic fields emanating from solid-state samples. The quantum sensor does so with unprecedented d.c. sensitivity at micrometre resolution, from room to cryogenic temperatures. An additional advantage of the SQCRAMscope is the preservation of optical access to the sample so that magnetometry imaging of, for example, electron transport may be performed in concert with other imaging techniques. Here, we apply this multimodal imaging capability to the study of nematicity in iron pnictide high-temperature superconductors, where the relationship between electronic and structural symmetry breaking resulting in a nematic phase is under debate. We combine the SQCRAMscope with an in situ microscope that measures optical birefringence near the surface. This enables simultaneous and spatially resolved detection of both bulk and near-surface manifestations of nematicity via transport and structural deformation channels, respectively. By performing local measurements of emergent resistivity anisotropy in iron pnictides, we observe sharp, nearly concurrent transport and structural transitions. More broadly, these measurements demonstrate the SQCRAMscope’s ability to reveal important insights into the physics of complex quantum materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Designing Energy-Efficient Quantum Computers Through Prediction and Reduction of Cooling Requirements for Cryogenic Electronics

Quantum computing has been identified as a “wild card” by the International Energy Agency in predicting future global data center energy usage. This is primarily because both uncertainty in the extent to which quantum computing will be adopted, and uncertainty in the power consumption of individual quantum data centers. Unlike the classical counterparts, quantum computers need to be maintained at near absolute zero, requiring energy-intensive cryogenic cooling systems. Therefore, as quantum computers scale up from existing 50 qubit technology demonstrations to the 10,000 to 100,000 qubit systems that will be able to solve complex problems, the energy consumption of both the electronics and the required cooling systems will also increase. To predict this scaling, this work analyzes the energy requirements for both computation and cooling of quantum hardware. We show that the energy requirements for cooling of quantum computers is determined by several computing system parameters, including the number and type of physical qubits, the operating temperature, the packaging efficiency of the system, and the split between circuits operating at cryogenic temperatures and those operating at room temperature. The energy requirements can then be found based on thermal system parameters such as cooling efficiency and cryostat heat transfer. Analysis of these parameters shows that the energy required for cooling is significantly larger than that required for computation, a reversal from energy usage patterns seen in conventional computing. The results and discussions provide a road-map for creating energy efficient quantum computers through the selection of computer architectures and cryogenic system configurations that minimize cooling requirements.

energy efficiency↗
DOE OSTI2022

Investigation of Microwave Transducers for Linearity Dependence and Applications in Quantum Networking

Quantum devices have the potential to revolutionize applications in computing, communications, and sensing; however, current state-of-art resources must operate at extremely low temperatures, making the routing of microwave control and readout signals challenging to scale. Interest in microwave photonic solutions to this problem has grown in recent years, in which control signals are delivered to the cold stage via optical fiber, where they are converted to electrical signals through photodetection. Overall link performance depends strongly on the characteristics of the photodiode, yet detailed measurements of many detector properties remain lacking at cold temperatures. In this work, we examine and compare the performance of a modified uni-traveling carrier photodiode (MUTC-PD) at both room (300 K) and liquid nitrogen (80 K) temperatures, focusing in particular on responsivity, bandwidth, and linearity. In line with previous work, we find a sharp reduction in responsivity at 1550 nm as temperature decreases, while RF bandwidth remains steady. Interestingly, our linearity tests reveal that the RF output saturates more quickly at 80 K, suggesting reduced linearity with lower temperature, the cause of which is still under investigation. Our results should help contribute to the understanding and future design of highly linear cryogenic quantum links.

Bolton, Summer↗
DOE OSTI2023

Cryogenic Control Circuitry for Superconducting Qubits

Superconducting qubits have reached the point where system designers are worried about the heat that control wiring brings into the cryostat. To continue scaling cryogenic quantum systems, control solutions that work inside the cold space must be explored. One possibility is to use control electronics that is native to superconductivity, so called single-flux-quantum (SFQ) circuitry, to form an interface between qubits and whatever other electronics is needed to control eventual quantum systems. To begin exploring the utility of SFQ as control circuitry, we performed modeling and experiments on qubit readout using ballistic fluxons which are SFQ in the limit of ballistic fluxon transport. Our modeling results show that a flavor of qubit, the fluxonium, can be read out using ballistic fluxons. We designed test samples to prove some of the key concepts needed for such a readout but were ultimately unable to getting a working demonstration. The lack of testing success was due to challenges in fabrication and running short of time to perform testing rather than a fundamental problem with our analysis.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Scalable low-loss cryogenic packaging of quantum memories in CMOS-foundry processed photonic chips

Optically linked solid-state quantum memories such as color centers in diamond are a promising platform for distributed quantum information processing and networking. Photonic integrated circuits (PICs) have emerged as a crucial enabling technology for these systems, integrating quantum memories with efficient electrical and optical interfaces in a compact and scalable platform. Packaging these hybrid chips into deployable modules while maintaining low optical loss and resiliency to temperature cycling is a central challenge to their practical use. We demonstrate a packaging method for PICs using surface grating couplers and angle-polished fiber arrays that is robust to temperature cycling, offers scalable channel count, applies to a wide variety of PIC platforms and wavelengths, and offers pathways to automated high-throughput packaging. Using this method, we show optically and electrically packaged quantum memory modules integrating all required qubit controls on chip, operating at millikelvin temperatures with <3 dB losses achievable from fiber to quantum memory for the TE 0 mode at a wavelength of 737 nm.

Bernson, Robert [Tyndall National Institute, Cork ↗
DOE OSTI2023

Emergent Quantum Magnetism and Cryogenic Spin-Memory in Twisted Bilayer Graphene

Recently developed techniques for assembling moiré heterostructures have enabled unprecedented control of the interlayer interactions within the heterostructure, allowing for the realization of strongly correlated electronic states. The experimentally realized states, to date, include a variety of topological states, superconductivity, and strange metal behavior. However, the phenomenology varies significantly from sample to sample. Here we will present microscopy techniques for further characterization of both the progenitor exfoliated materials and the composite moiré heterostructure. The application of these techniques has allowed for an unprecidented degree of characterization in ambient conditions. Additionally we will explore the use of resistively detected electron spin resonance (ESR) as a novel probe for spin order in moirés. While our results do not show clearly dispersive features that would unambiguously evince spin excitations within the sample, the technique is still promising.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Ultra low noise materials and devices for cryogenic superconductors and quantum bits

Materials, products, methods of use and fabrication thereof are disclosed. The materials are particularly well suited for application in products such as superconducting devices and quantum computing, due to ability to avoid undesirable effects from inherent noise and decoherence. The materials are formed from select isotopes having zero nuclear spin into a single crystal-phase film or layer of thickness depending on the desired application of the resulting device. The film/layer may be suspended or disposed on a substrate. The isotopes may be enriched from naturally-occurring sources of isotopically mixed elemental material(s). The single crystal is preferably essentially devoid of structural defects such as grain boundaries, inclusions, impurities and lattice vacancies.

Pereverzev, Sergey↗