  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 quantum-enhanced 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.
