F. E. Becerra

Demonstrating highly symmetric single-mode, single-photon heralding efficiency in spontaneous parametric downconversion

We demonstrate a symmetric, single-spatial mode, single-photon heralding efficiency of 84% for a type-II spontaneous parametric downconversion process. High efficiency, single-spatial mode collection is key to enabling many quantum information processing and quantum metrology applications.

Correlated photon pairs generated from a warm atomic ensemble

We present measurements of the cross-correlation function of photon pairs at 780 nm and 1367 nm, generated in a hot rubidium vapor cell. The temporal character of the biphoton is determined by the dispersive properties of the medium where the pair generation takes place. We show that short correlation times occur for optically thick samples, which can be understood in terms of offresonant pair generation. By modifying the linear response of the sample, we produce near-resonant photon pairs, which could in principle be used for entanglement distribution.

Photon statistics and polarization correlations at telecommunications wavelengths from a warm atomic ensemble.

We present measurements of the polarization correlation and photon statistics of photon pairs that emerge from a laser-pumped warm rubidium vapor cell. The photon pairs occur at 780 nm and 1367 nm and are polarization entangled. We measure the autocorrelation of each of the generated fields as well as the cross-correlation function, and observe a strong violation of the two-beam Cauchy-Schwartz inequality. We evaluate the performance of the system as source of heralded single photons at a telecommunication wavelength. We measure the heralded autocorrelation and see that coincidences are suppressed by a factor of ≈ 20 from a Poissonian source at a generation rate of 1500 s(-1), a heralding efficiency of 10%, and a narrow spectral width.

Photon-number-resolved detection of photon-subtracted thermal light.

We examine the photon statistics of photon-subtracted thermal light with photon-number-resolving detection. We show the photon-number distribution transforming from a Bose-Einstein distribution to a Poisson distribution as the number of subtracted photon increases.

Direct measurement of sub-wavelength interference using thermal light and photon-number-resolved detection

We examine thermal light diffracted through a double slit using photon-number-resolved detection to directly measure high-order spatial correlations, and we see sinusoidal modulations of those correlations. The fringe width can, in principal, be made arbitrarily small, and we have experimentally obtained fringe widths as small as 30 nm with 800 nm wavelength light. This extreme sub-wavelength resolution, along with this direct detection technique, offers potential for high precision measurement applications.

Multi-state discrimination below the quantum noise limit at the single-photon level

Measurements approaching the ultimate quantum limits of sensitivity are central in quantum information processing, quantum metrology, and communication. Quantum measurements to discriminate multiple states at the single-photon level are essential for optimizing information transfer in low-power optical communications and quantum communications, and can enhance the capabilities of many quantum information protocols. Here, we theoretically investigate and experimentally demonstrate the discrimination of multiple coherent states of light with sensitivities surpassing the quantum noise limit (QNL) at the single-photon level under realistic conditions of loss and noise based on strategies implementing globally-optimized adaptive measurements with single photon counting and displacement operations. These discrimination strategies can provide realistic advantages to enhance information transfer at low powers, and are compatible with photon number resolving detection, which provides robustness at high powers, thus allowing for surpassing the QNL at arbitrary input power levels under realistic conditions.Quantum measurements: surpassing conventional sensitivity limits at low powersLight has intrinsic quantum noise, which limits how well we can measure it, especially at low powers, and bounds how much information we can communicate. A team led by F. Elohim Becerra at the University of New Mexico demonstrated optimized measurements for light pulses with different phases at low powers, such as those used in coherent optical communication. These optimized measurements can surpass the ultimate sensitivity limits of ideal conventional detectors, even in the presence of loss and noise encountered in realistic situations. The measurements are based on combining the input pulse with a reference field, and counting single photons in a fraction of the pulse. By analyzing the detection outcome, the reference field can be optimized to enhance the measurement’s sensitivity. Optimized measurements at low powers may lead to more-efficient optical communication in realistic environments.

State discrimination signal nulling receivers

Optimized state-discrimination receiver strategies for nonorthogonal states can improve the capacity of the communication channels operating with error rates below the ones corresponding to conventional receivers. Coherent signal-nulling receivers use a local oscillator to null the signal state and perform the discrimination of the signal from an alphabet of nonorthogonal states. We describe our study of signal nulling for signals encoded in nonorthogonal phase states. The signal nulling discrimination setup is the first step for the experimental investigation of different discrimination strategies for receivers of coherent multi-phase encoded signals.

Demonstrating high symmetric single-mode single-photon heralding efficiency in spontaneous parametric downconversion

We demonstrate a symmetric, single-spatial mode, single-photon heralding efficiency of 84% for a type-II spontaneous parametric downconversion process. High efficiency, single-spatial mode collection is key to enabling many quantum information processing and quantum metrology applications.

Beating the standard quantum limit for nonorthogonal multi-state discrimination

We demonstrate a quantum receiver that discriminates four nonorthogonal states with error probabilities below the standard quantum limit (SQL) for a wide range of input powers and as much as 6 dB below the SQL.