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Register a new userRobust Majorana signature detection with a coupled quantum dot-nanomechanical resonator in all-optical domain
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Motivated by a recent experiment [Nadj-Perge et al., Science 346, 602 (2014)] providing evidence for Majorana zero modes in iron chains on the superconducting Pb surface, in the present work, we theoretically propose an all-optical scheme to detect Majorana fermions, which is very different from the current tunneling measurement based on electrical means. The optical detection proposal consists of a quantum dot embedded in a nanomechanical resonator with optical pump-probe technology. With the optical means, the signal in the coherent optical spectrum presents a distinct signature for the existence of Majorana fermions in the end of iron chains. Further, the vibration of the nanomechanical resonator behaving as a phonon cavity will enhance the exciton resonance spectrum, which makes the Majorana fermions more sensitive to be detectable. This optical scheme affords a potential supplement for detection of Majorana fermions and supports to use Majorana fermions in Fe chains as qubits for potential applications in quantum computing devices.
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We propose a current correlation spectrum approach to probe the quantum behaviors of a nanome-chanical resonator (NAMR). The NAMR is coupled to a double quantum dot (DQD), which acts as a quantum transducer and is further coupled to a quantum-point contact (QPC). By measuring the current correlation spectrum of the QPC, shifts in the DQD energy levels, which depend on the phonon occupation in the NAMR, are determined. Quantum behaviors of the NAMR could, thus, be observed. In particular, the cooling of the NAMR into the quantum regime could be examined. In addition, the effects of the coupling strength between the DQD and the NAMR on these energy shifts are studied. We also investigate the impacts on the current correlation spectrum of the QPC due to the backaction from the charge detector on the DQD.
We propose an approach for achieving ground-state cooling of a nanomechanical resonator (NAMR) capacitively coupled to a triple quantum dot (TQD). This TQD is an electronic analog of a three-level atom in $Lambda$ configuration which allows an electron to enter it via lower-energy states and to exit only from a higher-energy state. By tuning the degeneracy of the two lower-energy states in the TQD, an electron can be trapped in a dark state caused by destructive quantum interference between the two tunneling pathways to the higher-energy state. Therefore, ground-state cooling of an NAMR can be achieved when electrons absorb readily and repeatedly energy quanta from the NAMR for excitations.
We demonstrate a method of tuning a semiconductor quantum dot (QD) onto resonance with a cavity mode all-optically. We use a system comprised of two evanescently coupled cavities containing a single QD. One resonance of the coupled cavity system is used to generate a cavity enhanced optical Stark shift, enabling the QD to be resonantly tuned to the other cavity mode. A twenty-seven fold increase in photon emission from the QD is measured when the off-resonant QD is Stark shifted into the cavity mode resonance, which is attributed to radiative enhancement of the QD. A maximum tuning of 0.06 nm is achieved for the QD at an incident power of 88 {mu}W.
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We propose a three-terminal structure to probe robust signatures of Majorana zero modes consisting of a quantum dot coupled to the normal metal, s-wave superconducting and Majorana Y-junction leads. The zero-bias differential conductance at zero temperature of the normal-metal lead peaks at $2e^{2}/h$, which will be deflected after Majorana braiding. We find that the effect of thermal broadening is significantly suppressed when the dot is on resonance. In the case that the energy level of the quantum dot is much larger than the superconducting gap, tunneling processes are dominated by Majorana-induced crossed Andreev reflection. Particularly, a novel kind of crossed Andreev reflection equivalent to the splitting of charge quanta $3e$ occurs after Majorana braiding.
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