Miles P. Blencowe, Hui Wang
We describe how analogues of a Hawking evaporating black hole as well as the Unruh effect for an oscillatory, accelerating photodetector in vacuum may be realized using superconducting, microwave circuits that are fashioned out of Josephson tunnel junction and film bulk acoustic resonator elements.
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Magnetically-levitated superconducting microparticles have been recently proposed as a promising platform for performing quantum experiments with particles in the picogram regime. Here, we demonstrate the superconducting technology to achieve chip-based magnetic levitation of superconducting microparticles. We simulate and fabricate a chip-based magnetic trap capable of levitating superconducting particles with diameters from 0.5$\,μ$m to 200$\,μ$m. The trap consists of two stacked silicon chips, each patterned with a planar multi-winding superconducting coil made of niobium. The two coils gen…
Efficient flip-chip and on-chip-based modulation of flux-tunable superconducting resonators
本文提出了一种高效低电流磁通调制方法，利用翻转芯片和芯片内线圈实现超导谐振子的高灵敏度磁通检测。
This is a reply to the Comment on 'Spin Decoherence in Superconducting Atom Chips' [arXiv:quant-ph/0610095 (2006)].
Superconducting atom chips have very significant advantages in realizing trapping structures for ultracold atoms compared to conventional atom chips. We extend these advantages further by developing the ability to dynamically tailor the superconducting trap architecture. Heating the chosen parts of a superconducting film by transferring optical images onto its surface we are able to modify the current density distribution and create desired trapping potentials. This method enables us to change the shape and structure of magnetic traps, enabling versatile applications in atomtronics.
Quantum coherent feedback has been proven to be an efficient way to tune the dynamics of quantum optical systems and, recently, those of solid-state quantum circuits. Here, inspired by the recent progress of quantum feedback experiments, especially those in mesoscopic circuits, we prove that superconducting circuit QED systems, shunted with a coherent feedback loop, can change the dynamics of a superconducting transmission line resonator, i.e., a linear quantum cavity, and lead to strong on-chip nonlinear optical phenomena. We find that bistability can occur under the semiclassical approximati…
An on-chip microwave circulator that is compatible with superconducting devices is a key element for scale-up of superconducting circuits. Previous approaches to integrating circulators on chip involve either external driving that requires extra microwave lines or a strong magnetic field that would compromise superconductivity. Here we report the first proof-of-principle realisation of a passive on-chip circulator which is made from a superconducting loop interrupted by three notionally-identical Josephson junctions and is tuned with only DC control fields. Our experimental results shows evide…
Superconductors are considered in view of applications to atom chip devices. The main features of magnetic traps based on superconducting wires in the Meissner and mixed states are discussed. The former state may mainly be interesting for improved atom optics, while in the latter, cold atoms may provide a probe of superconductor phenomena. The properties of a magnetic side guide based on a single superconducting strip wire placed in an external magnetic field are calculated analytically and numerically. In the mixed state of type II superconductors, inhomogeneous trapped magnetic flux, relaxat…
Quantum feedback is a technique for measuring a qubit and applying appropriate feedback depending on the measurement results. Here, we propose a new on-chip quantum feedback method where the measurement-result information is not taken from the chip to the outside of a dilution refrigerator. This can be done by using a selective qubit-energy shift induced by measurement apparatus. We demonstrate on-chip quantum feedback and succeed in the rapid initialization of a qubit by flipping the qubit state only when we detect the ground state of the qubit. The feedback loop of our quantum feedback metho…
A superconducting on-chip microwave cavity for tunable hybrid systems with optically trapped Rydberg atoms
本文面向超导片上微波电路与光阱超冷原子混合系统，优化超导芯片和微波腔设计以实现对铷原子里德伯跃迁的可调谐强耦合，并通过实验表征腔特性，为在稀释制冷机中实现接近强耦合的混合量子平台奠定基础。
We propose a tunable on-chip micromaser using a superconducting quantum circuit (SQC). By taking advantage of externally controllable state transitions, a state population inversion can be achieved and preserved for the two working levels of the SQC and, when needed, the SQC can generate a single photon. We can regularly repeat these processes in each cycle when the previously generated photon in the cavity is decaying, so that a periodic sequence of single photons can be produced persistently. This provides a controllable way for implementing a persistent single-photon source on a microelectr…
We analyze the design of a potential replacement technology for the commercial ferrite circulators that are ubiquitous in contemporary quantum superconducting microwave experiments. The lossless, lumped element design is capable of being integrated on chip with other superconducting microwave devices, thus circumventing the many performance-limiting aspects of ferrite circulators. The design is based on the dynamic modulation of DC superconducting microwave quantum interference devices (SQUIDs) that function as nearly linear, tunable inductors. The connection to familiar ferrite-based circulat…
We report on the design and performance of an on-chip microwave circulator with a widely (GHz) tunable operation frequency. Non-reciprocity is created with a combination of frequency conversion and delay, and requires neither permanent magnets nor microwave bias tones, allowing on-chip integration with other superconducting circuits without the need for high-bandwidth control lines. Isolation in the device exceeds 20 dB over a bandwidth of tens of MHz, and its insertion loss is small, reaching as low as 0.9 dB at select operation frequencies. Furthermore, the device is linear with respect to i…
Quantum information processing holds great promise for communicating and computing data efficiently. However, scaling current photonic implementation approaches to larger system size remains an outstanding challenge for realizing disruptive quantum technology. Two main ingredients of quantum information processors are quantum interference and single-photon detectors. Here we develop a hybrid superconducting-photonic circuit system to show how these elements can be combined in a scalable fashion on a silicon chip. We demonstrate the suitability of this approach for integrated quantum optics by …
We have trapped rubidium atoms in the magnetic field produced by a superconducting atom chip operated at liquid Helium temperatures. Up to $8.2\cdot 10^5$ atoms are held in a Ioffe-Pritchard trap at a distance of 440 $μ$m from the chip surface, with a temperature of 40 $μ$K. The trap lifetime reaches 115 s at low atomic densities. These results open the way to the exploration of atom--surface interactions and coherent atomic transport in a superconducting environment, whose properties are radically different from normal metals at room temperature.
We study theoretically the lifetime of magnetically trapped atoms in the close vicinity of a type-II superconducting surface, in the context of superconducting atom-chips. We account for the magnetic noise created at the cloud position by the vortices present in the superconductor and give specific results for our experiment which uses a niobium film. Our main result is that atom losses are dominated by the presence of vortices. They remain however dramatically smaller than in equivalent room-temperature atom-chip setups using normal metals.
We present a detailed analysis of two chip-based superconducting trap architectures capable of levitating micrometer-sized superconducting particles in the Meissner state. These architectures are suitable for performing novel quantum experiments with more massive particles or for force and acceleration sensors of unprecedented sensitivity. We focus in our work on a chip-based anti-Helmholtz coil-type trap (AHC) and a planar double-loop (DLP) trap. We demonstrate their fabrication from superconducting Nb films and the fabrication of superconducting particles from Nb or Pb. We apply finite eleme…
We present a design for a superconducting, on-chip circulator composed of dynamically modulated transfer switches and delays. Design goals are set for the multiplexed readout of superconducting qubits. Simulations of the device show that it allows for low-loss circulation (insertion loss < 0.35 dB and isolation >20 dB) over an instantaneous bandwidth of 2.3 GHz. As the device is estimated to be linear for input powers up to -65 dBm, this design improves on the bandwidth and power-handling of previous superconducting circulators by over a factor of 50, making it ideal for integration with broad…
Quantum error correction can preserve quantum information in the presence of local errors, but correlated errors are fatal. For superconducting qubits, high-energy particle impacts from background radioactivity produce energetic phonons that travel throughout the substrate and create excitations above the superconducting ground state, known as quasiparticles, which can poison all qubits on the chip. We use normal metal reservoirs on the chip back side to downconvert phonons to low energies where they can no longer poison qubits. We introduce a pump-probe scheme involving controlled injection o…
Microwave circulators play an important role in quantum technology based on superconducting circuits. The conventional circulator design, which employs ferrite materials, is bulky and involves strong magnetic fields, rendering it unsuitable for integration on superconducting chips. One promising design for an on-chip superconducting circulator is based on a passive Josephson-junction ring. In this paper, we consider two operational issues for such a device: circuit tuning and the effects of quasiparticle tunneling. We compute the scattering matrix using adiabatic elimination and derive the par…
We propose and analyse a practically implementable scheme to generate macroscopic entanglement of a Bose-Einstein condensate in a micro-magnetic trap magnetically coupled to a superconducting loop. We treat the superconducting loop in a quantum superposition of two different flux states coupled with the magnetic trap to generate macroscopic entanglement. Our scheme also provides a platform to realise interferometry of entangled atoms through the Bose-Einstein condensate and to explore physics at the quantum-classical interface.
We study a quantum computing system using microwave photons in transmission line resonators on a superconducting chip as qubits. We show that all control necessary for quantum computing can be implemented by coupling to Josephson devices on the same chip, and take advantage of their strong inherent nonlinearities to realize qubit interactions. We analyze the gate error rate to demonstrate that our scheme is realistic even for Josephson devices with limited decoherence times. A conceptually innovative solution based on existing technologies, our scheme provides an integrated and scalable approa…
Experimentally verified, fast analytic and numerical design of superconducting resonators in flip-chip architectures
本文提出基于共形映射的解析方法，从二维截面快速预测超导谐振器参数，经三维模拟及15个倒装芯片谐振器实验验证，频率误差小于2%，并给出降低芯片间距敏感性的设计方法。
Localized Thermometry via Dayem Bridges Integrated on Superconducting Qubit Chips
研究超导量子比特芯片上的温度测量难题，利用集成的代姆桥，通过提取临界电流获取局部温度定量测量，经实验校准、验证及关联，确立其为低温硬件开发和超导量子电路片上测温的有效工具。
Neural Network-Based Frequency Optimization for Superconducting Quantum Chips
针对超导量子芯片频率配置的NP完全优化挑战，提出基于神经网络的频率配置方法，通过模型估计误差与局部优化策略寻找最优配置，并设计感知串扰的硬件高效拟设以提升变分量子求解器的能量计算。
We theoretically investigate the heating rate and spin flip lifetimes due to near field noise for atoms trapped close to layered superconducting structures. In particular, we compare the case of a gold layer deposited above a superconductor with the case of a bare superconductor. We study a niobium-based and a YBCO-based chip. For both niobium and YBCO chips at a temperature of 4.2 K, we find that the deposition of the gold layer can have a significant impact on the heating rate and spin flip lifetime, as a result of the increase of the near field noise. At a chip temperature of 77 K, this eff…
Deterministic quantum teleportation between distant superconducting chips
该研究通过64米长超低损耗电缆总线连接远距离超导芯片，利用飞行微波光子实现确定性量子态和纠缠门隐形传态，为分布式超导量子计算网络奠定基础。
Making analogy with atomic physics is a powerful tool for photonic technology, witnessed by the recent development in topological photonics and non-Hermitian photonics based on parity-time symmetry. Mollow triplet is a prominent atomic effect with both fundamental and technological importance. Here we demonstrate the analogue of Mollow triplet with quantum photonic systems. Photonic entanglement is generated with spontaneous nonlinear processes in dressed photonic modes, which are introduced through coherent multimode coupling. We further demonstrate the flexibility of the photonic system to r…
Spectroscopy is a powerful tool to probe physical, chemical, and biological systems. Recent advances in microfabrication have introduced novel, intriguing mesoscopic quantum systems including superconductor-semiconductor hybrid devices and topologically non-trivial electric circuits. A sensitive, general purpose spectrometer to probe the energy levels of these systems is lacking. We propose an on-chip absorption spectrometer functioning well into the millimeter wave band which is based on a voltage-biased superconducting quantum interference device. We demonstrate the capabilities of the spect…
Flexible Integration of Gigahertz Nanomechanical Resonators with a Superconducting Microwave Resonator using a Bonded Flip-Chip Method
本研究提出电流键合倒装芯片方法，实现吉赫兹纳米机械谐振器与可调超导微波谐振器的强耦合，在低温下获得约15 MHz耦合强度，为可即插即用的复杂杂化量子系统架构奠定基础。
The spatial correlation of radiation-induced errors in superconducting devices decays over a millimeter
本文利用六个同芯片超导谐振器的纳秒级多路复用读出构建片上地震阵列，通过声子差分飞行时间定位辐射撞击点，并揭示声子介导辐射污染在毫米尺度上衰减。
3D-Integrated Superconducting qubits: CMOS-Compatible, Wafer-Scale Processing for Flip-Chip Architectures
本文开发了CMOS兼容的3D集成超导量子比特，采用倒装芯片键合和200毫米晶圆加工，实现高良率激发和15微秒的弛豫时间。
Hybrid quantum systems involving cold atoms and microwave resonators can enable cavity-mediated infinite-range interactions between atomic spin systems and realize atomic quantum memories and transducers for microwave to optical conversion. To achieve strong coupling of atoms to on-chip microwave resonators, it was suggested to use atomic Rydberg states with strong electric dipole transitions. Here we report on the realization of coherent coupling of a Rydberg transition of ultracold atoms trapped on an integrated superconducting atom chip to the microwave field of an on-chip coplanar waveguid…
We comment on a recent paper [Phys. Rev. Lett. 97, 070401 (2006): quant-ph/0603229] concerning rubidium atoms trapped near a superconducting niobium surface at ~4K. This seeks to calculate the rate of atomic spin flips induced by thermal magnetic noise. We point out that the calculation is in error by a large factor because it is based on the two-fluid model of superconductivity. This model gives a poor description of electromagnetic dissipation just below the critical temperature because it cannot incorporate the case II coherences of a fuller quantum theory.
Using the inductive-energy participation ratio to characterize a superconducting quantum chip
提出感应能量参与比方法，高效提取超导量子芯片的线性和非线性参数及哈密顿量，推动量子电子设计自动化。
Superconducting surface trap chips for microwave-driven trapped ions
针对微波囚禁离子电极焦耳热阻碍门速度、保真度及可扩展性的问题，提出集成高Q微波谐振器的超导表面势阱芯片，利用超导Nb谐振器降低损耗，实现节能的双比特门方案。
We have integrated single and coupled superconducting transmon qubits into flip-chip modules. Each module consists of two chips -- one quantum chip and one control chip -- that are bump-bonded together. We demonstrate time-averaged coherence times exceeding $90\,μs$, single-qubit gate fidelities exceeding $99.9\%$, and two-qubit gate fidelities above $98.6\%$. We also present device design methods and discuss the sensitivity of device parameters to variation in interchip spacing. Notably, the additional flip-chip fabrication steps do not degrade the qubit performance compared to our baseline s…
Passive microwave circulation on a superconducting chip
针对超导量子电路中微波环形器体积庞大难以集成的问题，研究人员在超导芯片上实现了由三个隧道耦合超导岛构成、仅需直流控制的无源片上微波环形器，测得其具备良好的非互易散射性能与200 MHz带宽。
As the field of superconducting quantum computing advances from the few-qubit stage to larger-scale processors, qubit addressability and extensibility will necessitate the use of 3D integration and packaging. While 3D integration is well-developed for commercial electronics, relatively little work has been performed to determine its compatibility with high-coherence solid-state qubits. Of particular concern, qubit coherence times can be suppressed by the requisite processing steps and close proximity of another chip. In this work, we use a flip-chip process to bond a chip with superconducting …
Using a multi-layered printed circuit board, we propose a 3D architecture suitable for packaging supercon- ducting chips, especially chips that contain two-dimensional qubit arrays. In our proposed architecture, the center strips of the buried coplanar waveguides protrude from the surface of a dielectric layer as contacts. Since the contacts extend beyond the surface of the dielectric layer, chips can simply be flip-chip packaged with on-chip receptacles clinging to the contacts. Using this scheme, we packaged a multi-qubit chip and per- formed single-qubit and two-qubit quantum gate operation…
Solid state optical interconnect between distant superconducting quantum chips
本研究提出一种基于晶体电子自旋的量子接口，利用STIRAP操作实现超导磁通量子比特与光学腔之间的量子态交换，并通过光纤连接实现远距离超导量子比特间超过90%保真度的量子传输。
Using a consistent quantum-mechanical treatment for the electromagnetic radiation, we theoretically investigate the magnetic spin-flip scatterings of a neutral two-level atom trapped in the vicinity of a superconducting body. We derive a simple scaling law for the corresponding spin-flip lifetime for such an atom trapped near a superconducting thick slab. For temperatures below the superconducting transition temperature T_c, the lifetime is found to be enhanced by several orders of magnitude in comparison to the case of a normal conducting slab. At zero temperature the spin-flip lifetime is gi…
Coherent interface between optical and microwave photons on an integrated superconducting atom chip
本文提出利用单层亚波长原子阵列作为可切换镜面，在集成超导芯片上实现光学光子与微波光子的相干接口，通过驱动激光耦合里德堡态，利用微波光子的存在与否控制原子阵列对入射光脉冲的透明或反射状态。
We propose and analyze a passive architecture for realizing on-chip, scalable cascaded quantum devices. In contrast to standard approaches, our scheme does not rely on breaking Lorentz reciprocity. Rather, we engineer the interplay between pairs of superconducting transmon qubits and a microwave transmission line, in such a way that two delocalized orthogonal excitations emit (and absorb) photons propagating in opposite directions. We show how such cascaded quantum devices can be exploited to passively probe and measure complex many-body operators on quantum registers of stationary qubits, thu…
Low crosstalk modular flip-chip architecture for coupled superconducting qubits
本文提出一种低串扰模块化倒装芯片架构，通过电浮动芯片实现耦合超导量子比特的简单组装，并验证了横向耦合开关比约50、zz串扰约0.7 kHz及隔离度>60 dB的性能。
Accurate gap control of 3D-integrated superconducting quantum circuits using asymmetric indium architecture and multi-angle flip-chip bonding
该研究针对倒装芯片三维集成超导量子电路的间隙控制问题，提出不对称铟结构结合多角度压缩的工艺，实现低损耗互连与高相干量子比特，将键合后平均倾斜降至(20±12)μrad，为三维集成超导量子处理器提供可行方案。
Sideband transitions are spectroscopically probed in a system consisting of a Cooper pair box strongly but non-resonantly coupled to a superconducting transmission line resonator. When the Cooper pair box is operated at the optimal charge bias point the symmetry of the hamiltonian requires a two photon process to access sidebands. The observed large dispersive ac-Stark shifts in the sideband transitions induced by the strong non-resonant drives agree well with our theoretical predictions. Sideband transitions are important in realizing qubit-photon and qubit-qubit entanglement in the circuit q…
We describe a scheme to coherently convert a microwave photon of a superconducting co-planar waveguide resonator to an optical photon emitted into a well-defined temporal and spatial mode. The conversion is realized by a cold atomic ensemble trapped above the surface of the superconducting atom chip, near the antinode of the microwave cavity. The microwave photon couples to a strong Rydberg transition of the atoms that are also driven by a pair of laser fields with appropriate frequencies and wavevectors for an efficient wave-mixing process. With only few thousand atoms in an ensemble of moder…
Single Flux Quantum-Based Digital Control of Superconducting Qubits in a Multi-Chip Module
本文提出一种多芯片模块架构，通过分离SFQ元件与量子比特并使用In凸点键合，有效抑制了声子介导的准粒子中毒，将基于SFQ的门错误率降低一个数量级至1.2(1)%，并指明进一步优化驱动电路带宽可使保真度逼近理论极限。
We propose to directly and quantum-coherently couple a superconducting transmon qubit to magnons - the quanta of the collective spin excitations, in a nearby magnetic particle. The magnet's stray field couples to the qubit via a superconducting quantum interference device (SQUID). We predict a resonant qubit-magnon exchange and a nonlinear radiation-pressure interaction that are both stronger than dissipation rates and tunable by an external flux bias. We additionally demonstrate a quantum control scheme that generates qubit-magnon entanglement and magnonic Schrödinger cat states with high fid…
Analogue black-white hole solitons in travelling wave parametric amplifiers with superconducting nonlinear asymmetric inductive elements
本研究证明SNAIL-TWPA中由KdV或mKdV方程描述的孤子可形成可调的模拟黑白洞事件视界对，并借助三波混频增强Hawking辐射观测前景。
Modular Superconducting Qubit Architecture with a Multi-chip Tunable Coupler
本研究提出一种基于悬浮可调谐耦合器的模块化超导量子比特架构，通过三种多芯片耦合器设计实现跨芯片量子比特交互，验证了零耦合条件与高保真双比特门操作且不损害相干性。
Chip-scale superconducting quantum gravimeter combining a SQUID, a transmon, and a nanomechanical resonator
本文提出一种芯片级超导重力仪，利用可调磁通transmon量子比特与高Q值纳米机械梁耦合，通过SQUID磁通调制量子比特频率，实现高带宽重力测量。
A switch capable of routing microwave signals at cryogenic temperatures is a desirable component for state-of-the-art experiments in many fields of applied physics, including but not limited to quantum information processing, communication and basic research in engineered quantum systems. Conventional mechanical switches provide low insertion loss but disturb operation of dilution cryostats and the associated experiments by heat dissipation. Switches based on semiconductors or microelectromechanical systems have a lower thermal budget but are not readily integrated with current superconducting…
We fabricate and characterize superconducting through-silicon vias and electrodes suitable for superconducting quantum processors. We measure internal quality factors of a million for test resonators excited at single-photon levels, on chips with superconducting vias used to stitch ground planes on the front and back sides of the chips. This resonator performance is on par with the state of the art for silicon-based planar solutions, despite the presence of vias. Via stitching of ground planes is an important enabling technology for increasing the physical size of quantum processor chips, and …
On-chip Frequency divider in superconducting quantum circuit
本文提出了一种超导量子电路中的频率分割方案，通过三体和两体相互作用实现微波光子频率分割，减少高频电缆占用。
Analysis of Superconducting Qubit Layouts Using InductEx
本文使用 InductEx 软件对超导铝双量子比特芯片进行全面分析，提取了量子比特频率、非谐性等关键设计参数以验证 transmon 设计原理，证明了该工具在量子电路布局优化中的适用性。
On-Chip Nonreciprocal Superconducting Frequency Multiplier for Cryogenic Millimeter-Wave Multiplexed Control
提出一种基于片上低温非互易时空周期约瑟夫森频率倍增器的频率复用毫米波超导量子比特架构，用单低频输入替代多条高频XY驱动线，抑制Purcell衰变并减少98%以上串扰，使超过25个量子比特阵列的保真度维持在容错阈值以下。
We propose an experimental setup to test the role of curved spacetime on entanglement extraction from the vacuum of a quantum field to a pair of artificial atoms. In particular, we consider two superconducting qubits coupled to a dc-SQUID array embedded into an open microwave transmission line, where a suitable external bias is able to mimic a spacetime containing a traversable wormhole. We find that the amount of vacuum entanglement that can be extracted by the superconducting qubits depends on the parameters of the wormhole. At some distances qubits that would remain separable in flat spacet…
We propose and analyze an all-magnetic scheme to perform a Young's double slit experiment with a micron-sized superconducting sphere of mass $\gtrsim {10}^{13}$ amu. We show that its center of mass could be prepared in a spatial quantum superposition state with an extent of the order of half a micrometer. The scheme is based on magnetically levitating the sphere above a superconducting chip and letting it skate through a static magnetic potential landscape where it interacts for short intervals with quantum circuits. In this way, a protocol for fast quantum interferometry using quantum magneto…
Cryogenic Multiplexing Control Chip for Superconducting Quantum Processor
该研究提出一种低温多路复用控制芯片（MCC），可通过单根微波电缆控制多个超导量子比特，经仿真验证其性能，能减少微波控制线数量，助力大规模超导量子处理器研发。
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