54 research outputs found
Tunable Quantum Beam Splitters for Coherent Manipulation of a Solid-State Tripartite Qubit System
Coherent control of quantum states is at the heart of implementing
solid-state quantum processors and testing quantum mechanics at the macroscopic
level. Despite significant progress made in recent years in controlling single-
and bi-partite quantum systems, coherent control of quantum wave function in
multipartite systems involving artificial solid-state qubits has been hampered
due to the relatively short decoherence time and lacking of precise control
methods. Here we report the creation and coherent manipulation of quantum
states in a tripartite quantum system, which is formed by a superconducting
qubit coupled to two microscopic two-level systems (TLSs). The avoided
crossings in the system's energy-level spectrum due to the qubit-TLS
interaction act as tunable quantum beam splitters of wave functions. Our result
shows that the Landau-Zener-St\"{u}ckelberg interference has great potential in
the precise control of the quantum states in the tripartite system.Comment: 24 pages, 3 figure
Detection of small single-cycle signals by stochastic resonance using a bistable superconducting quantum interference device
We propose and experimentally demonstrate detecting small single-cycle and
few-cycle signals by using the symmetric double-well potential of a radio
frequency superconducting quantum interference device (rf-SQUID). We show that
the response of this bistable system to single- and few-cycle signals has a
non-monotonic dependence on the noise strength. The response, measured by the
probability of transition from initial potential well to the opposite one,
becomes maximum when the noise-induced transition rate between the two stable
states of the rf-SQUID is comparable to the signal frequency. Comparison to
numerical simulations shows that the phenomenon is a manifestation of
stochastic resonance.Comment: 5 pages 3 figure
Experimental demonstrations of high-Q superconducting coplanar waveguide resonators
We designed and successfully fabricated an absorption-type of superconducting
coplanar waveguide (CPW) resonators. The resonators are made from a Niobium
film (about 160 nm thick) on a high-resistance Si substrate, and each resonator
is fabricated as a meandered quarter-wavelength transmission line (one end
shorts to the ground and another end is capacitively coupled to a through
feedline). With a vector network analyzer we measured the transmissions of the
applied microwave through the resonators at ultra-low temperature (e.g., at 20
mK), and found that their loaded quality factors are significantly high, i.e.,
up to 10^6. With the temperature increases slowly from the base temperature
(i.e., 20 mK), we observed the resonance frequencies of the resonators are blue
shifted and the quality factors are lowered slightly. In principle, this type
of CPW-device can integrate a series of resonators with a common feedline,
making it a promising candidate of either the data bus for coupling the distant
solid-state qubits or the sensitive detector of single photons.Comment: Accepted by Chinese Science Bulleti
NLP-based detection of systematic anomalies among the narratives of consumer complaints
We develop an NLP-based procedure for detecting systematic nonmeritorious
consumer complaints, simply called systematic anomalies, among complaint
narratives. While classification algorithms are used to detect pronounced
anomalies, in the case of smaller and frequent systematic anomalies, the
algorithms may falter due to a variety of reasons, including technical ones as
well as natural limitations of human analysts. Therefore, as the next step
after classification, we convert the complaint narratives into quantitative
data, which are then analyzed using an algorithm for detecting systematic
anomalies. We illustrate the entire procedure using complaint narratives from
the Consumer Complaint Database of the Consumer Financial Protection Bureau
Quantum Dynamics of a Microwave Driven Superconducting Phase Qubit Coupled to a Two-Level System
We present an analytical and comprehensive description of the quantum
dynamics of a microwave resonantly driven superconducting phase qubit coupled
to a microscopic two-level system (TLS), covering a wide range of the external
microwave field strength. Our model predicts several interesting phenomena in
such an ac driven four-level bipartite system including anomalous Rabi
oscillations, high-contrast beatings of Rabi oscillations, and extraordinary
two-photon transitions. Our experimental results in a coupled qubit-TLS system
agree quantitatively very well with the predictions of the theoretical model.Comment: 6 pages, 3 figure
Observation of coherent oscillation in single-passage Landau-Zener transitions
Landau-Zener transition (LZT) has been explored in a variety of physical
systems for coherent population transfer between different quantum states. In
recent years, there have been various proposals for applying LZT to quantum
information processing because when compared to the methods using ac pulse for
coherent population transfer, protocols based on LZT are less sensitive to
timing errors. However, the effect of finite range of qubit energy available to
LZT based state control operations has not been thoroughly examined. In this
work, we show that using the well-known Landau-Zener formula in the vicinity of
an avoided energy-level crossing will cause considerable errors due to coherent
oscillation of the transition probability in a single-passage LZT experiment.
The data agree well with the numerical simulations which take the transient
dynamics of LZT into account. These results not only provide a closer view on
the issue of finite-time LZT but also shed light on its effects on the quantum
state manipulation.Comment: 10 pages,5 figure
Landau-Zener-St\"{u}ckelberg Interference of Microwave Dressed States of a Superconducting Phase Qubit
We present the first observation of Landau-Zener-St\"{u}ckelberg (LZS)
interference of the dressed states arising from an artificial atom, a
superconducting phase qubit, interacting with a microwave field. The dependence
of LZS interference fringes on various external parameters and the initial
state of the qubit agrees quantitatively very well with the theoretical
prediction. Such LZS interferometry between the dressed states enables us to
control the quantum states of a tetrapartite solid-state system with ease,
demonstrating the feasibility of implementing efficient multipartite quantum
logic gates with this unique approach.Comment: 6 pages, 3 figures To appear in Physical Review B(R
Quantum interference induced by multiple Landau-Zener transitions in a strongly driven rf-SQUID qubit
We irradiated an rf-SQUID qubit with large-amplitude and high frequency
electromagnetic field. Population transitions between macroscopic distinctive
quantum states due to Landau-Zener transitions at energy-level avoided
crossings were observed. The qubit population on the excited states as a
function of flux detuning and microwave power exhibits interference patterns.
Some novel features are found in the interference and a model based on rate
equations can well address the features.Comment: 6 pages, 3 figures, comments are welcom
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