Embedding a χ(2) crystal in a Fabry-Perot cavity, we propose and demonstrate an all-optical switch via quantum Zeno blockade that is implemented without any physical coupling between the signal and pump waves.
We propose an interaction-free scheme for all-optical switching which does not rely on the physical coupling between signal and control waves. The interaction-free nature of the scheme allows it to overcome the fundamental photon-loss limit imposed by the signal-pump coupling. The same phenomenon protects photonic-signal states from decoherence, making devices based on this scheme suitable for quantum applications. Focusing on $\ensuremath{\chi}{}^{(2)}$ waveguides, we provide device designs for traveling-wave and Fabry-Perot switches. In both designs, the performance is optimal when the signal switching is induced by coherent dynamical evolution. In contrast, when the switching is induced by a rapid dissipation channel, it is less efficient.
Abstract : All-optical switching is crucial for efficient optical communications. The quantum Zeno effect can be used to induce or inhibit optical switching through a variety of processes, all of which share the common characteristic that the evolution of one quantum state into another be inhibited or induced based on the presence or absence of a controllable and continuous quantum measurement. By utilizing this effect, it is the goal of this project to design and construct ultra-low power dissipation, ultra-low volume, fast all-optical switches. In particular, a fundamental limit in existing all-optical switching devices is due to the photon loss resulting from signal-pump coupling. When extended to the quantum domain, this photon loss additionally causes the quantum states of photonic signals to collapse (i.e., decohere). By using the quantum Zeno effect (QZE), it is possible to realize interaction-free switching that eliminates direct signal-pump coupling i.e., QZE for all-optical switching.
When overlapping in an optical medium with nonlinear susceptibility, light waves can interact with each other, changing their phases, wavelengths, shapes, and so on. Such nonlinear effects, discovered over a half century ago, have given rise to a breadth of important applications. Applying to quantum-mechanical signals, however, they face fundamental challenges arising from the multimode nature of the interacting electromagnetic fields, such as phase noises and Raman scattering. Quantum Zeno blockade allows strong interaction of light waves without them physically overlapping, thus providing a viable solution for those challenges, as indicated in recent bulk-optics experiments. Here, we report on the observation of quantum Zeno blockade on chip, where a light wave is modulated by another in a distinct "interaction-free" manner. For quantum applications, we also verify its operations on a single-photon level. Our results promise a scalable platform for overcoming several grand challenges faced by nonlinear optics and quantum information processing, enabling, e.g., manipulation and interaction of quantum signals without decoherence.
Overlapping in an optical medium with nonlinear susceptibilities, lightwaves can interact, changing each other's phase, wavelength, waveform shape, or other properties. Such nonlinear optical phenomena, discovered over a half-century ago, have led to a breadth of important applications. Applied to quantum-mechanical signals, however, these phenomena face fundamental challenges that arise from the multimodal nature of the interaction between the electromagnetic fields, such as phase noises and spontaneous Raman scattering. The quantum Zeno blockade allows strong interaction between lightwaves without physical overlap between them, thus offering a viable solution for the aforementioned challenges, as indicated in recent bulk-optics experiments. Here, we report on the observation of quantum Zeno blockade on chip, where a lightwave is modulated by another in a distinct "interaction-free" manner. For quantum applications, we also verify its operations on single-photon signals. Our results promise a scalable platform for overcoming several longstanding challenges in applied nonlinear and quantum optics, enabling manipulation and interaction of quantum signals without decoherence.
Quantum Zeno blockade allows all-optical switching in a counterintuitive “interaction-free” manner. Using a lithium-niobate microdisk cavity nanofabricated on chip, we have observed phase matched sum-frequency generation and interaction-free switching between optical pulses in two tightly confined whispering-gallery modes. We have also verified that our device is suitable for nonlinear operations in a single-photon regime. Our results point to a scalable, chip-integrated platform for nonlinear optics extendable to the quantum regime.