9 research outputs found
Energy efficient mining on a quantum-enabled blockchain using light
We outline a quantum-enabled blockchain architecture based on a consortium of
quantum servers. The network is hybridised, utilising digital systems for
sharing and processing classical information combined with a fibre--optic
infrastructure and quantum devices for transmitting and processing quantum
information. We deliver an energy efficient interactive mining protocol enacted
between clients and servers which uses quantum information encoded in light and
removes the need for trust in network infrastructure. Instead, clients on the
network need only trust the transparent network code, and that their devices
adhere to the rules of quantum physics. To demonstrate the energy efficiency of
the mining protocol, we elaborate upon the results of two previous experiments
(one performed over 1km of optical fibre) as applied to this work. Finally, we
address some key vulnerabilities, explore open questions, and observe
forward--compatibility with the quantum internet and quantum computing
technologies.Comment: 25 pages, 5 figure
Collisional-model quantum trajectories for entangled qubit environments
We study the dynamics of quantum systems interacting with a stream of
entangled qubits. Under fairly general conditions, we present a detailed
framework describing the conditional dynamical maps for the system, called
quantum trajectories, when the qubits are measured. Depending on the
measurement basis, these quantum trajectories can be jump-type or
diffusive-type, and they can exhibit features not present with quantum optical
and single-qubit trajectories. As an example, we consider the case of two
remote atoms, where jump-type quantum trajectories herald the birth and death
of entanglement.Comment: 25 pages, 6 figure
Experimental optical phase measurement approaching the exact Heisenberg limit
The use of quantum resources can provide measurement precision beyond the
shot-noise limit (SNL). The task of ab initio optical phase measurement---the
estimation of a completely unknown phase---has been experimentally demonstrated
with precision beyond the SNL, and even scaling like the ultimate bound, the
Heisenberg limit (HL), but with an overhead factor. However, existing
approaches have not been able---even in principle---to achieve the best
possible precision, saturating the HL exactly. Here we demonstrate a scheme to
achieve true HL phase measurement, using a combination of three techniques:
entanglement, multiple samplings of the phase shift, and adaptive measurement.
Our experimental demonstration of the scheme uses two photonic qubits, one
double passed, so that, for a successful coincidence detection, the number of
photon-passes is . We achieve a precision that is within of the HL,
surpassing the best precision theoretically achievable with simpler techniques
with . This work represents a fundamental achievement of the ultimate
limits of metrology, and the scheme can be extended to higher and other
physical systems.Comment: (12 pages, 6 figures), typos correcte