Superconducting quantum node for entanglement and storage of microwave radiation

Christopher Eichler

Emmanuel Flurin, Nicolas Roch, Jean-Damien Pillet +2 more

Superconducting circuits and microwave signals are good candidates to realize quantum networks, which are the backbone of quantum computers. We have realized a quantum node based on a 3D microwave superconducting cavity parametrically coupled to a transmission line by a Josephson ring modulator. We first demonstrate the time-controlled capture, storage, and retrieval of an optimally shaped propagating microwave field, with an efficiency as high as 80%. We then demonstrate a second essential ability, which is the time-controlled generation of an entangled state distributed between the node and a microwave channel.

A. H. Dayem, Rudolph Martin

Emmanuel Flurin, Nicolas Roch, Jean-Damien Pillet +3 more

This thesis work explores unique features offered by the Josephson mixer in the upcoming field of microwave quantum optics. We have demonstrated three major roles the Josephson mixer could play in emerging quantum information architectures. First, we have designed and fabricated a state-of-the-art practical quantum limited amplifier with the best quantum efficiency achieved to date. This tool is crucial for probing mesoscopic systems with microwaves, and in particular superconducting circuits. Hence, it has enabled us to realize successfully the stabilization of quantum trajectories of a superconducting qubit by measurement-based feedback. Second, we have shown how this circuit can generate and distribute entangled microwave radiations on separated transmission lines at different frequencies. Using two Josephson mixers, we have provided the first demonstration of entanglement between spatially separated propagating fields in the microwave domain, the so-called Einstein-Podolsky-Rosen states. Finally, we have used the Josephson mixer as a frequency converter. Acting as a switch, it is able to dynamically turn on and off the coupling to a low loss cavity. This feature allowed us to realize a quantum memory for microwaves. In combination with the ability to generate entanglement, we have measured the time-controlled generation, storage and on-demand release of an entangled state, which is a prerequisite for nodes of a quantum network.

Matti Partanen, Kirill G. Fedorov, Stefan Pogorzalek +5 more

Sergey A. Moiseev, F. F. Gubaidullin, Andrianov, S. N.

First solid state quantum computer was built using transmons (cooper pair boxes). The operation of the computer is limited because of using a number of the rigit cooper boxes working with fixed frequency at temperatures of superconducting material. Here, we propose a novel architecture of quantum computer based on a flexible wire circuit of many coupled quantum nodes containing controlled atomic (molecular) ensembles. We demonstrate wide opportunities of the proposed computer. Firstly, we reveal a perfect storage of external photon qubits to multi-mode quantum memory node and demonstrate a reversible exchange of the qubits between any arbitrary nodes. We found optimal parameters of atoms in the circuit and self quantum modes for quantum processing. The predicted perfect storage has been observed experimentally for microwave radiation on the lithium phthalocyaninate molecule ensemble. Then also, for the first time we show a realization of the efficient basic two-qubit gate with direct coupling of two arbitrary nodes by using appropriate atomic frequency shifts in the circuit nodes. Proposed two-qubit gate runs with a speed drastically accelerated proportionally to the number of atoms in the node. The direct coupling and accelerated two-qubit gate can be realized for large number of the circuit nodes. Finally, we describe two and three-dimensional scalable architectures that pave the road to construction of universal multi-qubit quantum computer operating at room temperatures.