Josephson radiation threshold detector

A Josephson radiation threshold detector (JRTD) that is based on the threshold behaviour of a current bias Josephson junction (CBJJ) is designed and fabricated for infrared radiation (IR@1550nm) detection at low temperatures. To achieve the optimal performance, we develop a binary hypothesis detection method to calibrate Josephson threshold behaviours (i.e. the switching current distributions of the CBJJ with the Al/AlOx/Al junction) in the absence and presence of radiation. In the absence of IR radiation, the junction transitioned with a measurable voltage drop across the junction, and this signal was treated as the events of hypothesis H0. The events of junction transition observed in the presence of the IR radiation served as hypothesis H1. Considering the usual Gaussian noise and based on statistical decision theory, the accumulated data of the measured switching current distributions are processed, and the threshold sensitivity of the demonstrated JRTD device is estimated. The minimum detectable IR radiation power of the proposed detector is approximately 0.74 pW, which corresponds to the photon rate of 5.692 × 106 photons/second. Further optimisation of JRTDs to implement the desired binary detection of a single photon is still a subject of argument, at least theoretically.

Sensitive enhancement of cat state quantum illumination

Quantum illumination is a binary hypothesis testing to detect a possible low-reflective object. Theoretically, both cat state illumination and Gaussian-state illumination possess the upper bound of 3dB sensitivity gain, over the usual coherent state illumination, for the significantly low illuminating intensity. Here, we investigate further how to enhance the quantum advantage of quantum illumination by optimizing the illuminating cat states for larger illuminating intensity. By comparing the quantum Fisher information or error exponent, we show that the sensitivity of the quantum illumination with generic cat states proposed here can be optimized further, and the 10.3% sensitive enhancement over the previous cat state illumination can be obtained.

Waveguide Mach-Zehnder interferometer to enhance the sensitivity of quantum parameter estimation

The waveguide Fabry-Perot interferometer (FPI) (see, e.g., in Phys. Rev. Lett.113, 243601 (2015)10.1103/PhysRevLett.115.243601 and Nature569, 692 (2019)10.1038/s41586-019-1196-1), instead of the free space's one, have been demonstrated for the sensitive quantum parameter estimations. Here, we propose a waveguide Mach-Zehnder interferometer (MZI) to further enhance the sensitivity of the relevant parameter estimations. The configuration is formed by two one-dimensional waveguides coupled sequentially to two atomic mirrors, which are served as the beam splitters of the waveguide photons to control the probabilities of the photons being transferred from one waveguide to another. Due to the quantum interference of the waveguide photons, the acquired phase of the photons when they pass through a phase shifter can be sensitively estimated by measuring either the transmitted or reflected probabilities of the transporting photons. Interestingly, we show that, with the proposed waveguide MZI the sensitivity of the quantum parameter estimation could be further optimized, compared with the waveguide FPI, in the same condition. The feasibility of the proposal, with the current atom-waveguide integrated technique, is also discussed.

Group delay controls of the photons transmitting through two cavities coupled by an artificial atomic ensemble: controllable electromagnetically induced transparency-like effects

As one of the typical quantum coherence phenomena, electromagnetically induced transparency (EIT) has been extensively applied to implement various quantum coherent manipulations, typically, e.g., optical quantum memories, photonic switches, and optical quantum computations, etc. By applying the input-output theory to the photonic transports through two cavities dispersively coupled by an artificial two-level atomic ensemble, we show here that the EIT-like effects could be observed. Particularly, the transparency windows and phase shift spectra of the transmitting photons could be engineered by manipulating the atomic levels in the ensemble to adjust the effective coupling strength between the cavities. As a consequence, the group delays of the transmitting photons can be manipulated by using the EIT-like effects. The proposal is demonstrated specifically with the experimental superconducting coplanar waveguide resonators coupled by the voltage-biased electrons on liquid Helium.

Quantum routings for single photons with different frequencies

Controllable single-photon routing takes the central roles in optical quantum networks for quantum information processing. Given that most of the schemes previously proposed are specifically designed for the photons with selected frequencies, here we investigate how to implement the routings of single photons with different frequencies. We show that the routing capabilities of the photons with different frequencies are manipulatable by properly designing the configuration of the scatters such as the cavity with embedded atoms and the channel boundaries. This is particularly important to implement the bandwidth routings of photons in future.

[Neuropathologic study of massive subcortical heterotopia]

Objective: To investigate the clinicpathologic features and probable mechanisms of massive subcortical heterotopia. Methods: Clinical data, histologic features and neuropathologic data were analyzed in five cases of massive subcortical heterotopia collected from Xuanwu Hospital, Capital Medical University from January 2014 to October 2017. Results: All five patients (three males and two females) had a history of refractory epilepsy with a mean period of 15.4 years (range 7 to 21 years). The median age at surgery was 28.6 years(range 20 to 39 years). Magnetic resonance imaging showed that the lesions were located in the temporal lobe (two cases), parietal lobe (one case), both temporal and occipital lobes (one case) and both temporal and parietal lobes (one case). Pathologic examination disclosed that massive gray matter in subcortical and deep white matter with various shape and size. Moreover, one case also showed subpial and periventricular heterotopias and polymicrogyria. Polymicrogyria or hippocampal sclerosis were seen in the remaining three cases. None of the five patients experienced seizure attacks during the follow-up period. Conclusions: Heterotopia is malformations due to abnormal neuronal migration. Massive subcortical heterotopia due to widespread abnormal neuronal migration is relatively rare. The mechanism of heterotopia together with polymicrogyria needs further discussion.

[Quality of life of patients with nonfunctioning pituitary adenoma: a meta-analysis]

OBJECTIVE

To evaluate the quality of life (QoL) of patients with nonfunctioning pituitary adenoma (NFPA) after systematic treatment.

METHODS

We searched all published articles involving in the QoL of patients with NFPA on line, and analyzed the results by the Revman5.3 software.

RESULTS

Five studies met the criteria of meta-analysis.The results of meta-analysis wereas follows: Physical function MD=0.76, 95%CI (-4.13, 5.64 ), P=0.76; Physical prole MD=-2.05, 95%CI (-7.41, 3.31), P=0.45; Body pain MD=3.50, 95%CI (1.11, 5.90), P=0.004; General health MD=-7.19, 95%CI (-12.77, -1.61), P=0.01; Vatility MD=-3.48, 95%CI (-7.39, 0.43), P=0.08; Social function MD=-4.64, 95%CI (-6.99, -2.38), P<0.000 1; Mental health MD=-0.05, 95%CI (-2.30, 2.20), P=0.96; Role emotion MD=-5.08, 95%CI (-8.20, -1.91), P=0.002.

CONCLUSIONS

This meta-analysisindicated thatthe QoL of patients with NFPA was damaged on the dimensions of general health, social function and role emotion.The dimension of physical painin patients with NFPA was better than that in general population, and there was no difference between other health dimensions.

A tunable coupler for superconducting microwave resonators using a nonlinear kinetic inductance transmission line

We present a tunable coupler scheme that allows us to tune the coupling strength between a feedline and a superconducting resonator in situ over a wide range. In this scheme, we shunt the feedline with a 50-Ω lumped-element nonlinear transmission line made from a 20 nm NbTiN film. By injecting a DC current, the nonlinear kinetic inductance changes and the effective impedance shunting the resonator periodically varies from a short to an open, which tunes the coupling strength and coupling quality factor Qc . We have demonstrated Qc tuning over a factor of 40, between Qc ~ 5.5 × 104 and Qc ~ 2.3 × 106, for a 4.5 GHz resonator by applying a DC current less than 3.3 mA. Our tunable coupler scheme is easy to implement and may find broad applications in superconducting detector and quantum computing/information experiments.

Strong couplings between artificial atoms and terahertz cavities

An electron floating on liquid helium is proposed to be trapped (by a microelectrode set below the liquid helium) in a high-finesse terahertz (THz) cavity. The two lowest levels of the vertical motion of the electron act as a two-level "atom," which could resonantly interact with the THz cavity, and thus the famous Jaynes-Cummings model (JCM) and driven JCM could be implemented. The numerical results show that, for the typical parameters of the cavity and electrons on the surface of liquid helium, strong coupling between the artificial atom and the THz cavity could be obtained.

Controllable coherent population transfers in superconducting qubits for quantum computing

We propose an approach to coherently transfer populations between selected quantum states in one- and two-qubit systems by using controllable Stark-chirped rapid adiabatic passages. These evolution-time insensitive transfers, assisted by easily implementable single-qubit phase-shift operations, could serve as elementary logic gates for quantum computing. Specifically, this proposal could be conveniently demonstrated with existing Josephson phase qubits. Our proposal can find an immediate application in the readout of these qubits. Indeed, the broken parity symmetries of the bound states in these artificial atoms provide an efficient approach to design the required adiabatic pulses.

Probing tiny motions of nanomechanical resonators: classical or quantum mechanical?

We propose a spectroscopic approach to probe tiny vibrations of a nanomechanical resonator (NAMR), which may reveal classical or quantum behavior depending on the decoherence-inducing environment. Our proposal is based on the detection of the voltage-fluctuation spectrum in a superconducting transmission line resonator (TLR), which is indirectly coupled to the NAMR via a controllable Josephson qubit acting as a quantum transducer. The classical (quantum mechanical) vibrations of the NAMR induce symmetric (asymmetric) Stark shifts of the qubit levels, which can be measured by the voltage fluctuations in the TLR. Thus, the motion of the NAMR, including if it is quantum mechanical or not, could be probed by detecting the voltage-fluctuation spectrum of the TLR.

Generation and control of Greenberger-Horne-Zeilinger entanglement in superconducting circuits

Going beyond the entanglement of microscopic objects (such as photons, spins, and ions), here we propose an efficient approach to produce and control the quantum entanglement of three macroscopic coupled superconducting qubits. By conditionally rotating, one by one, selected Josephson-charge qubits, we show that their Greenberger-Horne-Zeilinger (GHZ) entangled states can be deterministically generated. The existence of GHZ correlations between these qubits could be experimentally demonstrated by effective single-qubit operations followed by high-fidelity single-shot readouts. The possibility of using the prepared GHZ correlations to test the macroscopic conflict between the noncommutativity of quantum mechanics and the commutativity of classical physics is also discussed.

Controllable coupling between flux qubits

We propose an experimentally realizable method to control the coupling between two flux qubits. In our proposal, the bias fluxes are always fixed for these two inductively coupled qubits. The detuning of these two qubits can be initially chosen to be sufficiently large, so that their initial interbit coupling is almost negligible. When a variable frequency or time-dependent magnetic flux (TDMF) is applied to one of the qubits, a well-chosen frequency of the TDMF can be used to compensate the initial detuning and to couple two qubits. This proposed method avoids fast changes of either qubit frequencies or the amplitudes of the bias magnetic fluxes through the qubit loops, and also offers a remarkable way to implement any logic gate, as well as tomographically measure flux qubit states.

Optical selection rules and phase-dependent adiabatic state control in a superconducting quantum circuit

We analyze the optical selection rules of the microwave-assisted transitions in a flux qubit superconducting quantum circuit (SQC). We show that the parities of the states relevant to the superconducting phase in the SQC are well defined when the external magnetic flux phi(e) = phi(0)/2; then the selection rules are the same as the ones for the electric-dipole transitions in usual atoms. When phi(e) does not = phi(0)/2, the symmetry of the potential of the artificial "atom" is broken, a so-called delta-type "cyclic" three-level atom is formed, where one- and two-photon processes can coexist. We study how the population of these three states can be selectively transferred by adiabatically controlling the electromagnetic field pulses. Different from lambda-type atoms, the adiabatic population transfer in our three-level delta atom can be controlled not only by the amplitudes but also by the phases of the pluses.