Spin chains have long been considered an effective medium for long-range interactions, entangleme... more Spin chains have long been considered an effective medium for long-range interactions, entanglement generation, and quantum state transfer. In this work, we explore the properties of a spin chain implemented with superconducting flux circuits, designed to act as a connectivity medium between two superconducting qubits. The susceptibility of the chain is probed and shown to support long-range, cross-chain correlations. In addition, interactions between the two end qubits, mediated by the coupler chain, are demonstrated. This work has direct applicability in near term quantum annealing processors as a means of generating long-range, coherent coupling between qubits.
3D integration of superconducting quantum systems – part 3: Preserving qubit coherence
Bulletin of the American Physical Society, Mar 15, 2021
Cryogenic Qubit Integration for Quantum Computing
2018 IEEE 68th Electronic Components and Technology Conference (ECTC), 2018
We have demonstrated superconducting interconnect technologies that enable a variety of flip-chip... more We have demonstrated superconducting interconnect technologies that enable a variety of flip-chip 3D integrated structures and packages compatible with high-coherence superconducting qubits. Superconducting indium micro-bumps and underbump metal (UBM) were used to join superconducting qubit chips to superconducting readout and control modules while maintaining high qubit coherence (T1, T2, echo > 20 µs) in the presence of capacitive and inductive coupling between the chips. Scanning electron microscope, X-ray, infrared and confocal microscopy were used to investigate the micro-structure, alignment accuracy, and parallelism of flip-chip qubits. The superconducting readout and control modules can accommodate both niobium and aluminum-based circuit and amplifier fabrication processes, including shadow-evaporated aluminum or Nb/Al-AlOx/Nb trilayer Josephson junctions (JJs). We present results for up to 16 active superconducting chips having trilayer junctions bonded to a passive superconducting module. The I–V characteristics and switching behavior were measured for flip-chip-connected JJ arrays with 40-20,000 JJs. Our approach maintained chip-level junction critical current and qubit coherence, demonstrating it to be a viable approach to building larger quantum computing systems. This paper also discusses packaging approaches to developing a quantum-to-classical interface in a cryogenic environment with multiple temperature stages.
High-fidelity photon-number-resolution using multi-element superconducting nanowire single photon detectors
2008 Conference on Lasers and Electro-Optics and 2008 Conference on Quantum Electronics and Laser Science, 2008
Achieving photon-number-resolution using superconducting nanowire single photon detectors (SNSPDs... more Achieving photon-number-resolution using superconducting nanowire single photon detectors (SNSPDs) can enable high-speed source characterization and high-rate conditional state preparation. We report improved fidelity photon-number-resolution using high system-detection-efficiency four-element SNSPDs.
Tunable XX-Coupling Between High Coherence Flux Qubits
Bulletin of the American Physical Society, 2018
High-density cryogenic wiring for superconducting qubits
Superconducting circuits have emerged as a promising platform to build quantum processors. The ch... more Superconducting circuits have emerged as a promising platform to build quantum processors. The challenge of designing a circuit is to compromise between realizing a set of performance metrics and reducing circuit complexity and noise sensitivity. At the same time, one needs to explore a large design space, and computational approaches often yield long simulation times. Here we automate the circuit design task using SCILLA, a software for automated discovery of superconducting circuits. SCILLA performs a parallelized, closed-loop optimization to design circuit diagrams that match pre-defined properties such as spectral features and noise sensitivities. We employ it to discover 4-local couplers for superconducting flux qubits and identify a circuit that outperforms an existing proposal with similar circuit structure in terms of coupling strength and noise resilience for experimentally accessible parameters. This work demonstrates how automated discovery can facilitate the design of co...
With quantum computers being out of reach for now, quantum simulators are the alternative devices... more With quantum computers being out of reach for now, quantum simulators are the alternative devices for efficient and more exact simulation of problems that are challenging on conventional computers. Quantum simulators are classified into analog and digital, with the possibility of constructing “hybrid” simulators by combining both techniques. In this paper, we focus on analog quantum simulators of open quantum systems and address the limit that they can beat classical computers. In particular, as an example, we discuss simulation of the chlorosome light-harvesting antenna from green sulfur bacteria with over 250 phonon modes coupled to each electronic state. Furthermore, we propose physical setups that can be used to reproduce the quantum dynamics of a standard and multiple-mode Holstein model. The proposed scheme is based on currently available technology of superconducting circuits consist of flux qubits and quantum oscillators.
As superconducting qubit circuits become more complex, addressing a large array of qubits becomes... more As superconducting qubit circuits become more complex, addressing a large array of qubits becomes a challenging engineering problem. Dense arrays of qubits benefit from, and may require, access via the third dimension to alleviate interconnect crowding. Through-silicon vias (TSVs) represent a promising approach to three-dimensional (3D) integration in superconducting qubit arrays—provided they are compact enough to support densely-packed qubit systems without compromising qubit performance or low-loss signal and control routing. In this work, we demonstrate the integration of superconducting, high-aspect ratio TSVs—10 μm wide by 20 μm long by 200 μm deep—with superconducting qubits. We utilize TSVs for baseband control and high-fidelity microwave readout of qubits using a two-chip, bump-bonded architecture. We also validate the fabrication of qubits directly upon the surface of a TSV-integrated chip. These key 3D-integration milestones pave the way for the control and readout of hig...
Quantum annealing is an optimization technique which potentially leverages quantum tunneling to e... more Quantum annealing is an optimization technique which potentially leverages quantum tunneling to enhance computational performance. Existing quantum annealers use superconducting flux qubits with short coherence times, limited primarily by the use of large persistent currents Ip. Here, we examine an alternative approach, using qubits with smaller Ip and longer coherence times. We demonstrate tunable coupling, a basic building block for quantum annealing, between two flux qubits with small (∼ 50 nA) persistent currents. Furthermore, we characterize qubit coherence as a function of coupler setting and investigate the effect of flux noise in the coupler loop on qubit coherence. Our results provide insight into the available design space for next-generation quantum annealers with improved coherence.
With quantum computers being out of reach for now, quantum simulators are the alternative devices... more With quantum computers being out of reach for now, quantum simulators are the alternative devices for efficient and more exact simulation of problems that are challenging on conventional computers. Quantum simulators are classified into analog and digital, with the possibility of constructing "hybrid" simulators by combining both techniques. In this paper, we focus on analog quantum simulators of open quantum systems and address the limit that they can beat classical computers. In particular, as an example, we discuss simulation of the chlorosome light-harvesting antenna from green sulfur bacteria with over 250 phonon modes coupled to each electronic state. Furthermore, we propose physical setups that can be used to reproduce the quantum dynamics of a standard and multiple-mode Holstein model. The proposed scheme is based on currently available technology of superconducting circuits consist of flux qubits and quantum oscillators.
Achieving high counting rates in superconducting nanowire single-photon detectors
2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, 2006
... Appl. Supercond. 13, 180-183, (2003). [3] KS Il'in, M. Lindgren, M. Currie, AD Semenov, ... more ... Appl. Supercond. 13, 180-183, (2003). [3] KS Il'in, M. Lindgren, M. Currie, AD Semenov, GN Gol'tsman, R. Sobolewski, SI Cherednichenko, and EM Gershenzon, “Picosecond hot-electron energy relaxation in NbN superconducting photodetectors ,” Appl. Phys. Lett. ...
The scalable application of quantum information science will stand on reproducible and controllab... more The scalable application of quantum information science will stand on reproducible and controllable high-coherence quantum bits (qubits). Here , we revisit the design and fabrication of the superconducting flux qubit, achieving a planar device with broad frequency tunability, strong anharmonicity, high reproducibility, and relaxation times in excess of 40 µs at its flux-insensitive point. Qubit relaxation times 1 T across 22 qubits are consistently matched with a single model involving resonator loss, ohmic charge noise, and 1/f flux noise, a noise source previously considered primarily in the context of dephasing. We furthermore demonstrate that qubit dephasing at the flux-insensitive point is dominated by residual thermal photons in the readout resonator. The resulting photon shot noise is mitigated using a dynamical decoupling protocol, resulting in
Increasing Detection Efficiency of Superconducting Nanowire Single photon Detectors
ABSTRACT
Detectors Based on Superconductors
Experimental Methods in the Physical Sciences, 2013
ABSTRACT Superconducting materials provide a unique opportunity for single-photon detectors. The ... more ABSTRACT Superconducting materials provide a unique opportunity for single-photon detectors. The combination of the strong non-linearity present in the superconducting-metal transition and in Josephson junctions; the unique electrical property of zero resistance; the fast relaxation processes present in many superconducting materials; and the easily engineered optical absorptance of metals results in a system that can be adapted to many photo-detection requirements. As a result of these material features, a variety of detector families have emerged in recent years based on superconducting nanowires, tunnel junctions, weak thermal links, and kinetic-inductive resonators. The detectors variously provide high speed single-photon detection; high-sensitivity in the infrared, optical, UV, or even x-ray wavelengths; and high efficiency. The resulting applications include quantum and classical high-data-rate communication, biological imaging, LIDAR, and VLSI circuit evaluation among others.
Progress towards a metastable superconducting qubit 1 ANDREW KERMAN, WILLIAM OLIVER, VLADIMIR BOL... more Progress towards a metastable superconducting qubit 1 ANDREW KERMAN, WILLIAM OLIVER, VLADIMIR BOLKHOVSKY, MARK GOUKER, MIT Lincoln Laboratory -We will report on progress towards the demonstration of a metastable RF SQUID (MRFS) qubit, which has the potential to exhibit excited-state lifetimes many orders of magnitude longer than present-day superconducting qubits, while retaining long enough coherence times to allow gate error rates as low as ∼ 10 -5 . These properties result from the two main characteristics of the MRFS qubit: (i) its two lowest levels are essentially macroscopically distinct persistent-current states, which can be strongly decoupled from high-frequency electromagnetic fluctuations (in contrast to most superconducting qubits whose levels are approximately those of a nonlinear LC oscillator and are thus strongly coupled); and (ii) its extremely large inductance makes it only weakly sensitive to low-frequency magnetic flux noise.
Conference on Lasers and Electro-Optics 2010, 2010
We demonstrate the potential for 1.85 Mbit/s secure key rates over 101 km of fiber, >100 times fa... more We demonstrate the potential for 1.85 Mbit/s secure key rates over 101 km of fiber, >100 times faster than previously demonstrated, using the differential phase shift quantum key distribution protocol and superconducting nanowire single-photon detectors.
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