Receiver Operating Characteristics for a Prototype Quantum Two-Mode Squeezing Radar

Abstract

We have built and evaluated a prototype quantum radar, which we call a quantum two-mode squeezing radar (QTMS radar), in the laboratory. It operates solely at microwave frequencies; there is no downconversion from optical frequencies.Because the signal generation process relies on quantum mechanical principles, the system is considered to contain a quantumenhanced radar transmitter. This transmitter generates a pair of entangled microwave signals and transmits one of them through free space, where the signal is measured using a simple and rudimentary receiver.At the heart of the transmitter is a device called a Josephson parametric amplifier (JPA), which generates a pair of entangled signals called two-mode squeezed vacuum (TMSV) at 6.1445 GHz and 7.5376 GHz. These are then sent through a chain of amplifiers. The 7.5376 GHz beam passes through 0.5 m of free space; the 6.1445 GHz signal is measured directly after amplification. The two measurement results are correlated in order to distinguish signal from noise.We compare our QTMS radar to a classical radar setup using conventional components, which we call a two-mode noise radar (TMN radar), and find that there is a significant gain when both systems broadcast signals at −82 dBm. This is shown via a comparison of receiver operator characteristic (ROC) curves. In particular, we find that the quantum radar requires 8 times fewer integrated samples compared to its classical counterpart to achieve the same performance.

Quantum Two-Mode Squeezing Radar and Noise Radar: Correlation Coefficients for Target Detection

“…These expressions can be used to obtain an expression for the receiver operating characteristic (ROC) curve which would be obtained when the correlation coefficient is used as a detector function to distinguish whether a target is present or absent. Finally, we show that these expressions fit the experimental data obtained from the QTMS radar experiment described in [7].…”

“…Plot (a) shows how the curve changes with ρ, while (b) shows how it changes with N. The two plots cannot be directly compared because ρ and N are fundamentally different quantities, but they do suggest that increasing the correlation of the signals results in more dramatic gains than increasing the integration time. This can be seen from (7) as well: β effectively controls the width of the Rice distribution, and it decreases with the square root of N but quadratically with ρ. Of course, in practice certain tradeoffs need to be made between the two: increasing ρ may require designing and building entirely new radar systems, while increasing N indefinitely is impractical for many radar applications.…”

“…Entanglement causes the quantum noise between the two signals to be correlated, which allows us to achieve higher correlations. For more details on entanglement and quantum noise, see [7].…”

“…(Note that, for both QTMS radar and noise radar, the inphase and quadrature voltages are normally distributed with mean zero [7]- [9].) The problem is thatŜ is not guaranteed to be of the form (1) because (3) only constrains the resulting matrix to be positive semidefinite.…”

“…Quantum illumination radars [1]- [4], which are based on a phenomenon called entanglement, are a particularly well-studied class of quantum radars. An experimental implementation of a quantum two-mode squeezing (QTMS) radar, a variant of quantum illumination radar, was recently demonstrated [5]- [7]. Although it is not a full quantum radar (it uses amplifiers which break the entanglement), it demonstrates all the necessary ingredients of an entanglement-based radar, including the generation of an entangled signal and the transmission of microwaves through free space.…”