Weak signal detection using quantum interference

Iliya Esin, Alessandro Romito, Yuval Gefen

Quantum interference is typically detected through the dependence of the interference signal on certain parameters (path length, Aharonov-Bohm flux, etc.), which can be varied in a controlled manner. The destruction of interference by a which-path measurement is a paradigmatic manifestation of quantum effects. Here we report on a novel measurement protocol that realizes two objectives: (i) certifying that a measured signal is the result of interference avoiding the need to vary parameters of the underlying interferometer, and (ii) certifying that the interference signal at hand is of quantum nature. In particular, it yields a null outcome in the case of classical interference. Our protocol comprises measurements of cross-correlations between the readings of which-path weakly coupled detectors positioned at the respective interferometer's arms and the current in one of the interferometer's drains. We discuss its implementation with an experimentally available platform: an electronic Mach-Zehnder interferometer (MZI) coupled electrostatically to "detectors" (quantum point contacts).

David Finkelstein, Giuseppe Castagnoli

Davi Geiger, Zvi M. Kedem

Mevan Gunawardena

This thesis demonstrates the experimental implementation of a homodyne interference technique to detect weak atomic transitions. The demonstration of the technique uses two pathways to excite the cesium atom from its ground state to an excited state. One is a Stark-induced transition that is regulated by controlling a dc field across the cesium atoms. This is excited by a 411 nm laser field. A two-photon transition excited by an 822 nm laser field concurrently excites the same transition. The simultaneous excitation of the two pathways results in a quantum interference of the transition amplitudes. Phase modulating one of the beams gives rise to an amplitude modulation of the net excitation rate resulting in an amplitude modulated fluorescence signal. We observe the fluorescence at 794.6 nm due to the decay of the excited state to the ground state via an intermediate state. The strength of the amplitude modulation of the fluorescence signal is a measure of weak signal transition amplitude which in this demonstration is the controllable Stark-induced transition. Results of this work have shown improvements of two to three orders of magnitude in signal to noise over direct detection of the weak interaction. With possible improvements that are discussed it is projected to be much better.

Yin Zhang, Guowei Li, Junbo Wang +1 more

Spectral analysis technology in optical signal detection can obtain the spectral characteristics of matter according to the wavelength or frequency information of the optical signal. Commonly used spectral analysis techniques include grating spectrometer, Fourier transform infrared spectrometer (FTIR), Raman spectrometer, etc. In order to improve the measurement of optical signal, due to the limitation of detector detection bandwidth and system noise and external interference, this paper proposes an optical signal estimation scheme based on weak measurement method. Moreover, compared with the original weak measurement scheme, the detection time of the new scheme proposed in this paper breaks through the limitation of Nyquist sampling theorem, has the performance advantage of resisting aliasing interference, and can effectively improve the signal-to-noise ratio of the system by extending the detection time. This paper presents a new weak measurement theory scheme for optical signals. Theoretical research studies show that the scheme can estimate the amplitude and phase of the optical signal and recover the time domain by setting the dynamic phase factor with time for the previous or post-selection process. Because the detection time of the scheme is not limited by the Nyquist sampling theorem, the new scheme has the performance advantage of anti-aliasing interference, which effectively solves the limitation of the detector detection bandwidth in the original scheme.

Ivan B. Djordjević