NSA Will Use This III

Alternate headline: This will defeat NSA

New developments in quantum computing to fuel the cryptographic arms race...

Science News: Light breaks up to cloak gaps in time
Method could hide messages without sender's knowledge

Nature: A temporal cloak at telecommunication data rate

Through advances in metamaterials—artificially engineered media with exotic properties, including negative refractive index^{1, 2, 3}—the once fanciful invisibility cloak has now assumed a prominent place in scientific research^{4, 5, 6, 7, 8, 9, 10, 11, 12, 13}. By extending these concepts to the temporal domain¹⁴, investigators have recently described a cloak which hides events in time by creating a temporal gap in a probe beam that is subsequently closed up; any interaction which takes place during this hole in time is not detected¹⁵. However, these results are limited to isolated events that fill a tiny portion of the temporal period, giving a fractional cloaking window of only about 10⁻⁴ per cent at a repetition rate of 41 kilohertz (ref. 15)—which is much too low for applications such as optical communications. Here we demonstrate another technique for temporal cloaking, which operates at telecommunication data rates and, by exploiting temporal self-imaging through the Talbot effect, hides optical data from a receiver. We succeed in cloaking 46 per cent of the entire time axis and conceal pseudorandom digital data at a rate of 12.7 gigabits per second. This potential to cloak real-world messages introduces temporal cloaking into the sphere of practical application, with immediate ramifications in secure communications.


Science News: Quantum teleportation approaches the computer chip

The techniques laid out in two new studies are major steps toward developing quantum computers and ensuring secure communication over quantum networks...

Nature: Deterministic quantum teleportation of photonic quantum bits by a hybrid technique

Quantum teleportation¹ allows for the transfer of arbitrary unknown quantum states from a sender to a spatially distant receiver, provided that the two parties share an entangled state and can communicate classically. It is the essence of many sophisticated protocols for quantum communication and computation^{2, 3, 4, 5}. Photons are an optimal choice for carrying information in the form of ‘flying qubits’, but the teleportation of photonic quantum bits^{6, 7, 8, 9, 10, 11} (qubits) has been limited by experimental inefficiencies and restrictions. Main disadvantages include the fundamentally probabilistic nature of linear-optics Bell measurements¹², as well as the need either to destroy the teleported qubit or attenuate the input qubit when the detectors do not resolve photon numbers¹³. Here we experimentally realize fully deterministic quantum teleportation of photonic qubits without post-selection. The key step is to make use of a hybrid technique involving continuous-variable teleportation^{14, 15, 16} of a discrete-variable, photonic qubit. When the receiver’s feedforward gain is optimally tuned, the continuous-variable teleporter acts as a pure loss channel^{17, 18}, and the input dual-rail-encoded qubit, based on a single photon, represents a quantum error detection code against photon loss¹⁹ and hence remains completely intact for most teleportation events. This allows for a faithful qubit transfer even with imperfect continuous-variable entangled states: for four qubits the overall transfer fidelities range from 0.79 to 0.82 and all of them exceed the classical limit of teleportation. Furthermore, even for a relatively low level of the entanglement, qubits are teleported much more efficiently than in previous experiments, albeit post-selectively (taking into account only the qubit subspaces), and with a fidelity comparable to the previously reported values.

Nature: Deterministic quantum teleportation with feed-forward in a solid state system

Engineered macroscopic quantum systems based on superconducting electronic circuits are attractive for experimentally exploring diverse questions in quantum information science^{1, 2, 3}. At the current state of the art, quantum bits (qubits) are fabricated, initialized, controlled, read out and coupled to each other in simple circuits. This enables the realization of basic logic gates⁴, the creation of complex entangled states^{5, 6} and the demonstration of algorithms⁷ or error correction⁸. Using different variants of low-noise parametric amplifiers⁹, dispersive quantum non-demolition single-shot readout of single-qubit states with high fidelity has enabled continuous¹⁰ and discrete¹¹ feedback control of single qubits. Here we realize full deterministic quantum teleportation with feed-forward in a chip-based superconducting circuit architecture^{12, 13, 14}. We use a set of two parametric amplifiers for both joint two-qubit and individual qubit single-shot readout, combined with flexible real-time digital electronics. Our device uses a crossed quantum bus technology that allows us to create complex networks with arbitrary connecting topology in a planar architecture. The deterministic teleportation process succeeds with order unit probability for any input state, as we prepare maximally entangled two-qubit states as a resource and distinguish all Bell states in a single two-qubit measurement with high efficiency and high fidelity. We teleport quantum states between two macroscopic systems separated by 6 mm at a rate of 10⁴ s⁻¹, exceeding other reported implementations. The low transmission loss of superconducting waveguides is likely to enable the range of this and other schemes to be extended to significantly larger distances, enabling tests of non-locality and the realization of elements for quantum communication at microwave frequencies. The demonstrated feed-forward may also find application in error correction schemes.

Other developments...

Extreme-Tech: MIT discovers a new state of matter, a new kind of magnetism

Oregon State University: Electronics advance moves closer to a world beyond silicon