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Energy efficient optical tracking for space quantum communication

Eric Vokes, Vinod N. Rao, Elinore Spencer, Rupesh Kumar

Abstract

Power consumption is a critical constraint for CubeSat based quantum communication, where tracking systems often dominate the onboard power budget. We demonstrate an energy-efficient approach that enables reliable satellite tracking at substantially reduced beacon power by treating tracking as a weak-signal estimation task. Using a closed-loop system with fine steering mirrors and higher-order Kalman filters on ground, we can maintain stable tracking at a transmitted power equivalent to 34 mW over a -60 dB satellite to ground optical channel. Our results show that the resulting penalties on QKD bit error rates and signal-to-noise ratios are negligible, allowing for more efficient power allocation to quantum payloads in CubeSat missions.

Energy efficient optical tracking for space quantum communication

Abstract

Power consumption is a critical constraint for CubeSat based quantum communication, where tracking systems often dominate the onboard power budget. We demonstrate an energy-efficient approach that enables reliable satellite tracking at substantially reduced beacon power by treating tracking as a weak-signal estimation task. Using a closed-loop system with fine steering mirrors and higher-order Kalman filters on ground, we can maintain stable tracking at a transmitted power equivalent to 34 mW over a -60 dB satellite to ground optical channel. Our results show that the resulting penalties on QKD bit error rates and signal-to-noise ratios are negligible, allowing for more efficient power allocation to quantum payloads in CubeSat missions.
Paper Structure (14 sections, 23 equations, 9 figures)

This paper contains 14 sections, 23 equations, 9 figures.

Table of Contents

  1. Introduction
  2. Methods
  3. beacon Identification
  4. Camera calibration
  5. FSM calibration
  6. Emulating the satellite trajectory
  7. Kalman filter for constant velocity trajectory
  8. Kalman filter for an accelerating trajectory
  9. Estimation of QBER and excess noise
  10. Results
  11. Secret key fraction
  12. Discussions and conclusions
  13. Key rate for BB84 protocol
  14. Key rate for CV-QKD protocol

Figures (9)

  • Figure 1: Image depicting satellite pass over an OGS. Here the CubeSat involves the transmitter, that transmits signal to the OGS. The proposed QKD protocol involves tracking of CubeSat at a certain Zenith angle ($-30^\circ$), and then continue tracking until it reaches the last stage ($+30^\circ$).
  • Figure 2: Block diagram for emulating the tracking of satellite on a table top experiment. An oscillating mirror, driven by arbitrary waveform generator (AWG) displaces the beam where the FSM counteract the displacement. A computer connected to the camera acquires the frames, processes it and provides instructions to the FSM.
  • Figure 3: Progression of the image pre-processing pipeline used to clean the camera frame. (a) The raw, unprocessed frame. (b) The frame after dark frame subtraction, removing fixed-pattern noise. (c) The final output after applying morphological opening, showing the isolated laser signal.
  • Figure 4: The camera pixel mean intensity v/s laser beam power. The red and green dotted lines indicate the minimum and maximum laser intensities used during the tracking experiment, respectively.
  • Figure 5: FSM compensating the beam displacement for laser input power (a) $0.03\mu W$ and (b) $5.55\mu W$, respectively. Red shows the beam displacement action by the oscillating mirror while blue shows compensation by the FSM.
  • ...and 4 more figures