106 research outputs found
Controllable Entanglement Distribution Network Based on Silicon Quantum Photonics
The entanglement distribution network connects remote users through sharing
entanglement resources, which is essential for realizing quantum internet. We
proposed a controllable entanglement distribution network (c-EDN) based on a
silicon quantum photonic chip. The entanglement resources were generated by a
quantum light source array based on spontaneous four-wave mixing (SFWM) in
silicon waveguides and distributed to different users through time-reversed
Hong-Ou-Mandel interferences in on-chip Mach-Zehnder interferometers with
thermal phase shifters. A chip sample was designed and fabricated, supporting a
c-EDN with 3 subnets and 24 users. The network topology of entanglement
distributions could be reconfigured in three network states by controlling the
quantum interferences through the phase shifters, which was demonstrated
experimentally. Furthermore, a reconfigurable entanglement-based QKD network
was realized as an application of the c-EDN. The reconfigurable network
topology makes the c-EDN suitable for future quantum networks requiring
complicated network control and management. Moreover, it is also shows that
silicon quantum photonic chips have great potential for large-scale c-EDN,
thanks to their capacities on generating and manipulating plenty of
entanglement resources
Observation of entanglement negativity transition of pseudo-random mixed states
Multipartite entanglement is a key resource for quantum computation. It is
expected theoretically that entanglement transition may happen for multipartite
random quantum states, however, which is still absent experimentally. Here, we
report the observation of entanglement transition quantified by negativity
using a fully connected 20-qubit superconducting processor. We implement
multi-layer pseudo-random circuits to generate pseudo-random pure states of 7
to 15 qubits. Then, we investigate negativity spectra of reduced density
matrices obtained by quantum state tomography for 6 qubits.Three different
phases can be identified by calculating logarithmic negativities based on the
negativity spectra. We observe the phase transitions by changing the sizes of
environment and subsystems. The randomness of our circuits can be also
characterized by quantifying the distance between the distribution of output
bit-string probabilities and Porter-Thomas distribution. Our simulator provides
a powerful tool to generate random states and understand the entanglement
structure for multipartite quantum systems
Super-compact universal quantum logic gates with inversedesigned elements
Integrated quantum photonic circuit is a promising platform for the
realization of quantum information processing in the future. To achieve the
largescale quantum photonic circuits, the applied quantum logic gates should be
as small as possible for the high-density integration on chips. Here, we report
the implementation of super-compact universal quantum logic gates on silicon
chips by the method of inverse design. In particular, the fabricated
controlled-NOT gate and Hadamard gate are both nearly a vacuum wavelength,
being the smallest optical quantum gates reported up to now. We further design
the quantum circuit by cascading these fundamental gates to perform arbitrary
quantum processing, where the corresponding size is about several orders
smaller than that of previous quantum photonic circuits. Our study paves the
way for the realization of largescale quantum photonic chips with integrated
sources, and can possess important applications in the field of quantum
information processes
- …