13 research outputs found
Efficient High-dimensional Quantum Key Distribution with Hybrid Encoding
We propose a schematic setup of quantum key distribution (QKD) with an
improved secret key rate based on high-dimensional quantum states. Two
degrees-of-freedom of a single photon, orbital angular momentum modes, and
multi-path modes, are used to encode secret key information. Its practical
implementation consists of optical elements that are within the reach of
current technologies such as a multiport interferometer. We show that the
proposed feasible protocol has improved the secret key rate with much
sophistication compared to the previous 2-dimensional protocol known as the
detector-device-independent QKD.Comment: 10 pages, 6 figure
Bound for Gaussian-state Quantum illumination using direct photon measurement
We present bound for quantum illumination with Gaussian state when using
on-off detector or photon number resolving detector, where its performance is
evaluated with signal-to-noise ratio. First, in the case of coincidence
counting, the best performance is given by two-mode squeezed vacuum (TMSV)
state which outperforms coherent state and classically correlated thermal (CCT)
state. However coherent state can beat the TMSV state with increasing signal
mean photon number when using the on-off detector. Second, the performance is
enhanced by taking Fisher information approach of all counting probabilities
including non-detection events. In the Fisher information approach, the TMSV
state still presents the best performance but the CCT state can beat the TMSV
state with increasing signal mean photon number when using the on-off detector.
We also show that displaced squeezed state exhibits the best performance in the
single-mode Gaussian state.Comment: 5 pages, 2 figures, comments welcom
Gaussian Quantum Illumination via Monotone Metrics
Quantum illumination is to discern the presence or absence of a low
reflectivity target, where the error probability decays exponentially in the
number of copies used. When the target reflectivity is small so that it is hard
to distinguish target presence or absence, the exponential decay constant falls
into a class of objects called monotone metrics. We evaluate monotone metrics
restricted to Gaussian states in terms of first-order moments and covariance
matrix. Under the assumption of a low reflectivity target, we explicitly derive
analytic formulae for decay constant of an arbitrary Gaussian input state.
Especially, in the limit of large background noise and low reflectivity, there
is no need of symplectic diagonalization which usually complicates the
computation of decay constants. First, we show that two-mode squeezed vacuum
(TMSV) states are the optimal probe among pure Gaussian states with fixed
signal mean photon number. Second, as an alternative to preparing TMSV states
with high mean photon number, we show that preparing a TMSV state with low mean
photon number and displacing the signal mode is a more experimentally feasible
setup without degrading the performance that much. Third, we show that it is of
utmost importance to prepare an efficient idler memory to beat coherent states
and provide analytic bounds on the idler memory transmittivity in terms of
signal power, background noise, and idler memory noise. Finally, we identify
the region of physically possible correlations between the signal and idler
modes that can beat coherent states.Comment: 16 pages, 6 figure
A Method to Compute the Schrieffer–Wolff Generator for Analysis of Quantum Memory
Quantum illumination uses entangled light that consists of signal and idler modes to achieve higher detection rate of a low-reflective object in noisy environments. The best performance of quantum illumination can be achieved by measuring the returned signal mode together with the idler mode. Thus, it is necessary to prepare a quantum memory that can keep the idler mode ideal. To send a signal towards a long-distance target, entangled light in the microwave regime is used. There was a recent demonstration of a microwave quantum memory using microwave cavities coupled with a transmon qubit. We propose an ordering of bosonic operators to efficiently compute the Schrieffer–Wolff transformation generator to analyze the quantum memory. Our proposed method is applicable to a wide class of systems described by bosonic operators whose interaction part represents a definite number of transfer in quanta