One quanta

Jian Li, K Chalapat, Gheorghe Sorin Paraoanu

We study the problem of two superconducting quantum qubits coupled via a resonator. If only one quanta is present in the system and the number of photons in the resonator is measured with a null result, the qubits end up in an entangled Bell state. Here we look at one source of errors in this quantum nondemolition scheme due to the presence of more than one quanta in the resonator, previous to the measurement. By analyzing the structure of the conditional Hamiltonian with arbitrary number of quanta, we show that the scheme is remarkably robust against these type of errors. PACS:03.67.Lx,85.25.Cp,74.50.+r

David Finkelstein

Philip Ball

Jean-Paul Auffray, Mohamed Saladin El Naschie

In a recent publication in this journal one of us introduced the concept of “half quanta” and used it to provide a new insight into the origin and nature of the presence of dark energy in the cosmos. We investigate in the present note the possibility that, in spite of this success, the concept of half quanta should be regarded to be an illegitimate intruder in the realm of modern Quantum Physics.

Dan Ozawa, Yuki Yamanashi, Nobuyuki Yoshikawa

The lack of driving ability is one weakness of single-flux-quantum (SFQ) devices. At present, pulse splitters, which generate double or triple flux quanta from an SFQ input, are used when multiple-flux quanta (MFQ) must be obtained from an SFQ input. However, the splitter-based MFQ driver requires a very large circuit area and high latency. In order to overcome these problems, we investigated an MFQ driver using under-damped Josephson junctions. The advantage of the proposed MFQ driver is its current driving ability. The proposed MFQ driver can be used as a bit-line driver in an SFQ memory or as an output driver in a current-recycling system, which requires a large gain. The proposed MFQ driver was implemented using the ISTEC 2.5 kA/cm2Nb standard process (STP2), and its driving ability was investigated. We obtained a histogram of the output pulse number of the MFQ driver as a function of the bias current. In addition, we examined the propagation delay of the MFQ driver through circuit simulations. The results indicate that the MFQ driver can generate MFQ from an SFQ input more rapidly than splitter-based MFQ drivers.