I am going to post here all newly submitted articles on the arXiv related to superconducting circuits. If your article has been accidentally forgotten, feel free to contact me
11
Nov
2013
Entanglement-assisted electron microscopy based on a flux qubit
A notorious problem in high-resolution biological electron microscopy is radiation damage to the specimen caused by probe electrons. Hence, acquisition of data with minimal number of
electrons is of critical importance. Quantum approaches may represent the only way to improve the resolution in this context, but all proposed schemes to date demand delicate control of the electron beam in highly unconventional electron optics. Here we propose a scheme that involves a flux qubit based on a radio-frequency superconducting quantum interference device (rf-SQUID), inserted in essentially a conventional transmission electron microscope. The scheme significantly improves the prospect of realizing a quantum-enhanced electron microscope for radiation-sensitive specimens.
05
Nov
2013
Catching Shaped Microwave Photons with 99.4% Absorption Efficiency
Quantum information systems require high fidelity quantum operations. It is particularly challenging to convert flying qubits to stationary qubits for deterministic quantum networks,
since absorbing naturally shaped emission has a maximum fidelity of only 54%. Theoretical protocols reaching 100% efficiency rely upon sculpting the time dependence of photon wavepackets and receiver coupling. Using these schemes, experimental fidelities have reached up to 20% for optical photons and 81% for microwave photons, although with drive pulses much longer than the cavity decay rate. Here, we demonstrate a particularly simple „time reversed“ photon shape and gated receiver with an absorption fidelity of 99.4% and a receiver efficiency of 97.4% for microwave photons. We classically drive a superconducting coplanar waveguide resonator an order of magnitude shorter than the intrinsic decay time. With the fidelity now at the error threshold for fault tolerant quantum communication (96%) and computation (99.4%) and comparable to fidelities of good logic gates and measurements, new designs may be envisioned for quantum communication and computation systems.
01
Nov
2013
Quantum-limited amplification via reservoir engineering
We describe a new kind of phase-preserving quantum amplifier which utilizes dissipative interactions in a parametrically-coupled three-mode bosonic system. The use of dissipative interactions
provides a fundamental advantage over standard cavity-based parametric amplifiers: large photon number gains are possible with quantum-limited added noise, with no limitation on the gain-bandwidth product. We show that the scheme is simple enough to be implemented both in optomechanical systems and in superconducting microwave circuits.
Tunable slowing, storing and releasing of a weak microwave field
We study the slowing, storing and releasing of microwave pulses in a superconducting circuits composed of two coplanar waveguide resonators and a superconducting transmon-type qubit.
The quantum interference analogy to electromagnetically induced transparency is created in two coupled resonators. By tuning the resonance frequency of the transmon, we dynamically tune the effective coupling between the resonators. Via the modulation of the coupling, we show the tunable true time delay of microwave pulses at the single-photon level. We also store the microwave field in a high-Q resonator and release the signal from it to the output port. Our scheme promises applications in both quantum information processing and classical wireless communications.
30
Okt
2013
Hybrid quantum magnetism in circuit-QED: from spin-photon waves to many-body spectroscopy
We introduce a model of quantum magnetism induced by the non-perturbative exchange of microwave photons between distant superconducting qubits. By interconnecting qubits and cavities,
we obtain a spin-boson lattice model that exhibits a quantum phase transition where both qubits and cavities spontaneously polarise. We present a many-body ansatz that captures this phenomenon all the way, from a the perturbative dispersive regime where photons can be traced out, to the non-perturbative ultra-strong coupling regime where photons must be treated on the same footing as qubits. Our ansatz also reproduces the low-energy excitations, which are described by hybridised spin-photon quasiparticles, and can be probed spectroscopically from transmission experiments in circuit-QED, as shown by simulating a possible experiment by Matrix-Product-State methods.
28
Okt
2013
Linear response of superconducting flux quantum circuits
We study the microwave absorption of a driven three-level quantum system, which is realized by a superconducting flux quantum circuit (SFQC), with a magnetic driving field applied to
the two upper levels. The interaction between the three-level system and its environment is studied within the Born-Markov approximations, and we take into account the effects of the driving field on the damping rates of the three-level system. We study the linear response of the driven three-level SFQC to a weak probe field. The susceptibility of the probe field can be changed by both the driving field and the bias magnetic flux. When the bias magnetic flux is at the optimal point,the transition from the ground state to the second excited state is forbidden and the three-level system has a ladder-type transition. Thus, the SFQC responds to the probe field like natural atomic systems with ladder-type transitions. However, when the bias magnetic flux is away from the optimal point, the three-level SFQC has Δ-type transition, thus it responds to the probe field like a combination of natural atoms with ladder-type transitions and natural atoms with Λ-type transitions. In particular, we give detailed discussions on the conditions for realizing electromagnetically induced transparency and Autler-Townes splitting in three-level SFQCs.
24
Okt
2013
A single photon transistor based on superconducting systems
We present a realistic scheme for how to construct a single-photon transistor where the presence or absence of a single microwave photon controls the propagation of a subsequent strong
signal signal field. The proposal is designed to work with existing superconducting artificial atoms coupled to cavities. We study analytically and numerically the efficiency and the gain of our proposal and show that current transmon qubits allow for error probabilities ~1% and gains of the order of hundreds.
Tomography via Correlation of Noisy Measurement Records
We present methods and results of shot-by-shot correlation of noisy measurements to extract entangled state and process tomography in a superconducting qubit architecture. We show that
averaging continuous values, rather than counting discrete thresholded values, is a valid tomographic strategy and is in fact the better choice in the low signal-to-noise regime. We show that the effort to measure N-body correlations from individual measurements scales exponentially with N, but with sufficient signal-to-noise the approach remains viable for few-body correlations. We provide a new protocol to optimally account for the transient behavior of pulsed measurements. Despite single-shot measurement fidelity that is less than perfect, we demonstrate appropriate processing to extract and verify entangled states and processes.
15
Okt
2013
Photon Number Splitting of Squeezed Light by a Single Qubit in Circuit QED
We theoretically propose an efficient way to generate and detect squeezed light by a single qubit in circuit QED. By tuning the qubit energy splitting close to the fundamental frequency
of the first harmonic mode (FHM) in a transmission line resonator and placing the qubit at the nodal point of the third harmonic mode, one can generate the resonantly enhanced squeezing of the FHM upon pumping with the second harmonic mode. In order to investigate the photon number splitting for the squeezed FHM, we have numerically calculated the qubit absorption spectrum, which exhibits regularly spaced peaks at frequencies separated by twice the effective dispersive shift. It is also shown that adding a small pump field for the FHM makes additional peaks develop in between the dominant ones as well.
Hybrid Atom–Photon Quantum Gate in a Superconducting Microwave Resonator
We propose a novel hybrid quantum gate between an atom and a microwave photon in a superconducting coplanar waveguide cavity by exploiting the strong resonant microwave coupling between
adjacent Rydberg states. Using experimentally achievable parameters gate fidelities >0.99 are possible on sub-μs timescales for waveguide temperatures below 40 mK. This provides a mechanism for generating entanglement between two disparate quantum systems and represents an important step in the creation of a hybrid quantum interface applicable for both quantum simulation and quantum information processing.