Secure quantum remote state preparation of squeezed microwave states

Demonstration of microwave single-shot quantum key distribution

Security of modern classical data encryption often relies on computationally hard problems, which can be trivialized with the advent of quantum computers. A potential remedy for this is quantum communication which takes advantage of the laws of quantum physics to provide secure exchange of information. Here, quantum key distribution (QKD) represents a powerful tool, allowing for unconditionally secure quantum communication between remote parties. At the same time, microwave quantum communication is set to play an important role in future quantum networks because of its natural frequency compatibility with superconducting quantum processors and modern near-distance communication standards. To this end, we present an experimental realization of a continuous-variable QKD protocol based on propagating displaced squeezed microwave states. We use superconducting parametric devices for generation and single-shot quadrature detection of these states. We demonstrate unconditional security in our experimental microwave QKD setting. The security performance is shown to be improved by adding finite trusted noise on the preparation side. Our results indicate feasibility of secure microwave quantum communication with the currently available technology in both open-air (up to  ~ 80 m) and cryogenic (over 1000 m) conditions.

Scrutinizing joint remote state preparation under decoherence

This research examines the effect of an open system containing the squeezed generalized amplitude damping channel on the joint remote preparation quantum communication protocol using a maximally entangled two-qubit state. Our findings indicate that the fidelity of a quantum system in contact with a non-zero temperature thermal bath can be enhanced by varying the squeezing parameters. These parameters include the squeezing phase of the channel [Formula: see text] and the amount of squeezing of the channel r.

Remote switch for Schrödinger's cat state using Einstein-Podolsky-Rosen entanglement

We propose a 'remote switch' for Schrödinger's cat state (SCS). Resorting to nonlocal correlations, we demonstrate that an approximate SCS can be heralded at one mode of an Einstein-Podolsky-Rosen entangled state, via a conditional 'hybrid projective measurement' (HPM) performed on the other one mode. The HPM is able to fully manipulate both size and parity of the generated SCS. Here, the HPM consists of both photon number measurement and homodyne conditioning. Such a remote switch for SCS will open up new ideas in subsequent protocols, including fundamental tests and nonlocal manipulation of non-Gaussian states.

Remote preparation and manipulation of squeezed light

Remote state preparation enables one to create and manipulate a quantum state based on the shared entanglement between distant nodes. Here, we experimentally demonstrate remote preparation and manipulation of squeezed light. By performing a homodyne projective measurement on one mode of the continuous variable entangled state at Alice's station, a squeezed state is created at Bob's station. Moreover, rotation and displacement operations are applied on the prepared squeezed state by changing the projective parameters on Alice's state. We also show that the remotely prepared squeezed state is robust against loss and N - 1 squeezed states can be remotely prepared based on an N-mode continuous variable Greenberger-Horne-Zeilinger-like state. Our results verify the entanglement-based model used in security analysis of quantum key distribution with continuous variables and have potential application in remote quantum information processing.

Experimental Demonstration of Remotely Creating Wigner Negativity via Quantum Steering

Non-Gaussian states with Wigner negativity are of particular interest in quantum technology due to their potential applications in quantum computing and quantum metrology. However, how to create such states at a remote location remains a challenge, which is important for efficiently distributing quantum resource between distant nodes in a network. Here, we experimentally prepare an optical non-Gaussian state with negative Wigner function at a remote node via local non-Gaussian operation and shared Gaussian entangled state existing quantum steering. By performing photon subtraction on one mode, Wigner negativity is created in the remote target mode. We show that the Wigner negativity is sensitive to loss on the target mode, but robust to loss on the mode performing photon subtraction. This experiment confirms the connection between the remotely created Wigner negativity and quantum steering. As an application, we present that the generated non-Gaussian state exhibits metrological power in quantum phase estimation.

Experimental quantum teleportation of propagating microwaves

The field of quantum communication promises to provide efficient and unconditionally secure ways to exchange information, particularly, in the form of quantum states. Meanwhile, recent breakthroughs in quantum computation with superconducting circuits trigger a demand for quantum communication channels between spatially separated superconducting processors operating at microwave frequencies. In pursuit of this goal, we demonstrate the unconditional quantum teleportation of propagating coherent microwave states by exploiting two-mode squeezing and analog feedforward over a macroscopic distance of d = 0.42 m. We achieve a teleportation fidelity of F = 0.689 ± 0.004, exceeding the asymptotic no-cloning threshold. Thus, the quantum nature of the teleported states is preserved, opening the avenue toward unconditional security in microwave quantum communication.

Hybrid two-mode squeezing of microwave and optical fields using optically pumped graphene layers

A measurable quadrature of a squeezed quantum state manifests a small uncertainty below the Heisenberg limit. This phenomenon has the potential to enable several extraordinary applications in quantum information, metrology and sensing, and other fields. Several techniques have been implemented to realize squeezed electromagnetic states, including microwave fields and optical fields. However, hybrid squeezed modes (that incorporate both microwave and optical fields) have not yet been proposed despite their vital functionality to combine the two worlds of quantum superconducting systems and photonics systems. In this work, for the first time, we propose a novel approach to achieve two-mode squeezing of microwave and optical fields using graphene based structure. The proposed scheme includes a graphene layered structure that is driven by a quantum microwave voltage and subjected to two optical fields of distinct frequencies. By setting the optical frequency spacing equal to the microwave frequency, an interaction occurs between the optical and microwave fields through electrical modulation of the graphene conductivity. We show that significant hybrid two-mode squeezing, that includes one microwave field and one optical field, can be achieved. Furthermore, the microwave frequency can be tuned over a vast range by modifying the operation parameters.