659 research outputs found
Robust concurrent remote entanglement between two superconducting qubits
Entangling two remote quantum systems which never interact directly is an
essential primitive in quantum information science and forms the basis for the
modular architecture of quantum computing. When protocols to generate these
remote entangled pairs rely on using traveling single photon states as carriers
of quantum information, they can be made robust to photon losses, unlike
schemes that rely on continuous variable states. However, efficiently detecting
single photons is challenging in the domain of superconducting quantum circuits
because of the low energy of microwave quanta. Here, we report the realization
of a robust form of concurrent remote entanglement based on a novel microwave
photon detector implemented in the superconducting circuit quantum
electrodynamics (cQED) platform of quantum information. Remote entangled pairs
with a fidelity of are generated at Hz. Our experiment
opens the way for the implementation of the modular architecture of quantum
computation with superconducting qubits.Comment: Main paper: 7 pages, 4 figures; Appendices: 14 pages, 9 figure
Measurement-induced entanglement of two transmon qubits by a single photon
On-demand creation of entanglement between distant qubits is a necessary
ingredient for distributed quantum computation. We propose an entanglement
scheme that allows for single-shot deterministic entanglement creation by
detecting a single photon passing through a Mach-Zehnder interferometer with
one transmon qubit in each arm. The entanglement production essentially relies
on the fact that superconducting microwave structures allow to achieve strong
coupling between the qubit and the photon. By detecting the photon via a photon
counter, a parity measurement is implemented and the wave function of the two
qubits is projected onto a maximally entangled state. Most importantly, the
entanglement generation is heralded such that our protocol is not susceptible
to photon loss due to the indivisible nature of single photons.Comment: 18 pages, 2 figures; to be published in NJ
Freely Scalable Quantum Technologies using Cells of 5-to-50 Qubits with Very Lossy and Noisy Photonic Links
Exquisite quantum control has now been achieved in small ion traps, in
nitrogen-vacancy centres and in superconducting qubit clusters. We can regard
such a system as a universal cell with diverse technological uses from
communication to large-scale computing, provided that the cell is able to
network with others and overcome any noise in the interlinks. Here we show that
loss-tolerant entanglement purification makes quantum computing feasible with
the noisy and lossy links that are realistic today: With a modestly complex
cell design, and using a surface code protocol with a network noise threshold
of 13.3%, we find that interlinks which attempt entanglement at a rate of 2MHz
but suffer 98% photon loss can result in kilohertz computer clock speeds (i.e.
rate of high fidelity stabilizer measurements). Improved links would
dramatically increase the clock speed. Our simulations employed local gates of
a fidelity already achieved in ion trap devices.Comment: corrected typos, additional references, additional figur
Hong-Ou-Mandel interference of polarization qubits stored in independent room-temperature quantum memories
First generation quantum repeater networks require independent quantum
memories capable of storing and retrieving indistinguishable photons to perform
quantum-interference-mediated high-repetition entanglement swapping operations.
The ability to perform these coherent operations at room temperature is of
prime importance in order to realize large scalable quantum networks. Here we
address these significant challenges by observing Hong-Ou-Mandel (HOM)
interference between indistinguishable photons carrying polarization qubits
retrieved from two independent room-temperature quantum memories. Our
elementary quantum network configuration includes: (i) two independent sources
generating polarization-encoded qubits; (ii) two atomic-vapor dual-rail quantum
memories; and (iii) a HOM interference node. We obtained interference
visibilities after quantum memory retrieval of for few-photon level inputs and for single-photon level inputs. Our prototype
network lays the groundwork for future large-scale memory-assisted quantum
cryptography and distributed quantum networks.Comment: 12 pages, 6 figure
- …