198 research outputs found
Decoherence in adiabatic quantum evolution - application to Cooper pair pumping
One of the challenges of adiabatic control theory is the proper inclusion of
the effects of dissipation. Here, we study the adiabatic dynamics of an open
two-level quantum system deriving a generalized master equation to consistently
account for the combined action of the driving and dissipation. We demonstrate
that in the zero temperature limit the ground state dynamics is not affected by
environment. As an example, we apply our theory to Cooper pair pumping which
demonstrates the robustness of ground state adiabatic evolution.Comment: 7 pages, derivation of the master equation in the appendi
Quantum Circuits for General Multiqubit Gates
We consider a generic elementary gate sequence which is needed to implement a
general quantum gate acting on n qubits -- a unitary transformation with 4^n
degrees of freedom. For synthesizing the gate sequence, a method based on the
so-called cosine-sine matrix decomposition is presented. The result is optimal
in the number of elementary one-qubit gates, 4^n, and scales more favorably
than the previously reported decompositions requiring 4^n-2^n+1 controlled NOT
gates.Comment: 4 pages, 3 figure
Photon assisted tunneling as an origin of the Dynes density of states
We show that the effect of a high-temperature environment in current
transport through a normal metal-insulator-superconductor tunnel junction can
be described by an effective density of states (DOS) in the superconductor. In
the limit of a resistive low-ohmic environment, this DOS reduces into the
well-known Dynes form. Our theoretical result is supported by experiments in
engineered environments. We apply our findings to improve the performance of a
single-electron turnstile, a potential candidate for a metrological current
source.Comment: 4+3 pages, 4 figures; updated to the published version, includes
EPAPS supplementary materia
Lipreading and Covert Speech Production Similarly Modulate Human Auditory-Cortex Responses to Pure Tones
Watching the lips of a speaker enhances speech perception. At the same time, the 100 ms response to speech sounds is suppressed in the observer's auditory cortex. Here, we used whole-scalp 306-channel magnetoencephalography (MEG) to study whether lipreading modulates human auditory processing already at the level of the most elementary sound features, i.e., pure tones. We further envisioned the temporal dynamics of the suppression to tell whether the effect is driven by top-down influences. Nineteen subjects were presented with 50 ms tones spanning six octaves (125–8000 Hz) (1) during “lipreading,” i.e., when they watched video clips of silent articulations of Finnish vowels /a/, /i/, /o/, and /y/, and reacted to vowels presented twice in a row; (2) during a visual control task; (3) during a still-face passive control condition; and (4) in a separate experiment with a subset of nine subjects, during covert production of the same vowels. Auditory-cortex 100 ms responses (N100m) were equally suppressed in the lipreading and covert-speech-production tasks compared with the visual control and baseline tasks; the effects involved all frequencies and were most prominent in the left hemisphere. Responses to tones presented at different times with respect to the onset of the visual articulation showed significantly increased N100m suppression immediately after the articulatory gesture. These findings suggest that the lipreading-related suppression in the auditory cortex is caused by top-down influences, possibly by an efference copy from the speech-production system, generated during both own speech and lipreading.Peer reviewe
A Signal Processing Method to Explore Similarity in Protein Flexibility
Understanding mechanisms of protein flexibility is of great importance to structural biology. The ability to detect similarities between proteins and their patterns is vital in discovering new information about unknown protein functions. A Distance Constraint Model (DCM) provides a means to generate a variety of flexibility measures based on a given protein structure. Although information about mechanical properties of flexibility is critical for understanding protein function for a given protein, the question of whether certain characteristics are shared across homologous proteins is difficult to assess. For a proper assessment, a quantified measure of similarity is necessary. This paper begins to explore image processing techniques to quantify similarities in signals and images that characterize protein flexibility. The dataset considered here consists of three different families of proteins, with three proteins in each family. The similarities and differences found within flexibility measures across homologous proteins do not align with sequence-based evolutionary methods
A proposal for implementing an n-qubit controlled-rotation gate with three-level superconducting qubit systems in cavity QED
We present a way for implementing an n-qubit controlled-rotation gate with
three-level superconducting qubit systems in cavity QED. The two logical states
of a qubit are represented by the two lowest levels of each system while a
higher-energy level is used for the gate implementation. The method operates
essentially by preparing a state conditioned on the states of the control
qubits, creating a single photon in the cavity mode, and then performing an
arbitrary rotation on the states of the target qubit with assistance of the
cavity photon. It is interesting to note that the basic operational steps for
implementing the proposed gate do not increase with the number of qubits,
and the gate operation time decreases as the number of qubits increases. This
proposal is quite general, which can be applied to various types of
superconducting devices in a cavity or coupled to a resonator.Comment: Six figures, accepted by Journal of Physics: Condensed Matte
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