Entanglement-based quantum key distribution with a blinking-free quantum dot operated at a temperature up to 20 K

Christian Schimpf; Santanu Manna; Saimon F. Covre da Silva; Maximilian Aigner; Armando Rastelli

doi:10.1117/1.AP.3.6.065001

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Advanced Photonics
Vol. 3, Issue 6, 065001 (2021)

Entanglement-based quantum key distribution with a blinking-free quantum dot operated at a temperature up to 20 K | On the Cover

Christian Schimpf^†、*, Santanu Manna^*, Saimon F. Covre da Silva, Maximilian Aigner, and Armando Rastelli

Author Affiliations

Johannes Kepler University Linz, Institute of Semiconductor and Solid State Physics, Linz, Austria

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DOI: 10.1117/1.AP.3.6.065001 Cite this Article Set citation alerts

Christian Schimpf, Santanu Manna, Saimon F. Covre da Silva, Maximilian Aigner, Armando Rastelli. Entanglement-based quantum key distribution with a blinking-free quantum dot operated at a temperature up to 20 K[J]. Advanced Photonics, 2021, 3(6): 065001 Copy Citation Text

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$Photoluminescence properties of GaAs QDs in a p-i-n diode structure at a temperature of 20 K, excited by resonant TPE. (a) p-i-n diode structure with a tunnel barrier between the n-doped and the intrinsic regions. The inset shows the principle of TPE, with EP the laser energy, EB the biexciton (XX) binding energy, and S the exciton (X) FSS. (b) Emission spectra at TPE conditions when sweeping the diode voltage VP in forward bias. The inset shows the diode current I over VP. The white-dashed line indicates VP,0=0.3 V, at which the diode is operated during the QKD experiment. (c) Emission at VP=VP,0. (d) Second-order correlation function g(2) of the X signal with a time-bin of 1 μs at VP=VP,0. The g(2) is shown for the QD in the diode structure (red), indicating an on-time fraction of β=1.00(2) and a QD without diode (black, dashed) with a typical value of β≈0.3. (e) Wavelength shift and β for different deviations δVP=VP−VP,0. The blue-dashed line indicates a value of β corresponding to no blinking.$

Fig. 1. Photoluminescence properties of GaAs QDs in a p-i-n diode structure at a temperature of 20 K, excited by resonant TPE. (a) p-i-n diode structure with a tunnel barrier between the n-doped and the intrinsic regions. The inset shows the principle of TPE, with

E_{P}

the laser energy,

E_{B}

the biexciton (XX) binding energy, and

S

the exciton (X) FSS. (b) Emission spectra at TPE conditions when sweeping the diode voltage

V_{P}

in forward bias. The inset shows the diode current

I

over

V_{P}

. The white-dashed line indicates

V_{P, 0} = 0.3 V

, at which the diode is operated during the QKD experiment. (c) Emission at

V_{P} = V_{P, 0}

. (d) Second-order correlation function

g^{(2)}

of the X signal with a time-bin of

1 μ s

V_{P} = V_{P, 0}

. The

g^{(2)}

is shown for the QD in the diode structure (red), indicating an on-time fraction of

β = 1.00 (2)

and a QD without diode (black, dashed) with a typical value of

β \approx 0.3

. (e) Wavelength shift and

β

for different deviations

δ V_{P} = V_{P} - V_{P, 0}

. The blue-dashed line indicates a value of

β

corresponding to no blinking.

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Emission properties relevant for the polarization entanglement, measured at a temperature of 20 K. (a) Spectra of the individually filtered XX and X emission lines combined at a 50:50 fiber beam splitter. (b) Single-photon emission characteristics of the XX and X signals observed by detecting coincidences in a Hanbury–Brown–Twiss arrangement. The histogram for the X emission is shifted horizontally and vertically to facilitate reading. (c) Decay dynamics of the XX and X signals. The X signal exhibits a slow secondary decay channel, which is not present at temperatures lower than 10 K. (d) Examples among the 36 recorded coincidence histograms between the XX and X detections, corresponding to a measurement in the HV basis. The red-dashed lines indicate the time-bin of 2 ns, in which the coincidences are summed up to calculate the peak areas. (e) Unpolarized coincidence measurement between the XX and X photons. The excess coincidences at zero time delay stem from a nonunity photon-pair generation probability. (f) Density matrix of the two-photon polarization entangled state of the XX and X photons, recorded by full state tomography.

Fig. 2. Emission properties relevant for the polarization entanglement, measured at a temperature of 20 K. (a) Spectra of the individually filtered XX and X emission lines combined at a 50:50 fiber beam splitter. (b) Single-photon emission characteristics of the XX and X signals observed by detecting coincidences in a Hanbury–Brown–Twiss arrangement. The histogram for the X emission is shifted horizontally and vertically to facilitate reading. (c) Decay dynamics of the XX and X signals. The X signal exhibits a slow secondary decay channel, which is not present at temperatures lower than 10 K. (d) Examples among the 36 recorded coincidence histograms between the XX and X detections, corresponding to a measurement in the HV basis. The red-dashed lines indicate the time-bin of 2 ns, in which the coincidences are summed up to calculate the peak areas. (e) Unpolarized coincidence measurement between the XX and X photons. The excess coincidences at zero time delay stem from a nonunity photon-pair generation probability. (f) Density matrix of the two-photon polarization entangled state of the XX and X photons, recorded by full state tomography.

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Fig. 3. Key generation in the BBM92 protocol over a time span of about 8 h and entanglement-based QKD. (a) QKD arrangement. Alice and the photon source are situated on an optical table, and Bob is placed in a movable box on a table in another building and connected with the source via a 350-m long single mode fiber. (b) QBER during the key generation with an average of 8.42%. The red-dashed line marks the maximum allowed QBER for BBM92 in the infinite key regime. (c) Raw key rate (after key sifting) with an average of

54.8 bits / s

. (d) Encryption of a bitmap with the dimensions of

67 \times 70 pixels

and a color-depth of 4 bits, resulting in a total size of about 2.4 kilobytes. The encryption with Alice’s key yields a scrambled message ready to be sent over a public channel. (e) Decryption at Bob’s site when using an uncorrected key (left) and a corrected key (right).

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Temperature	5 K	20 K
X	XX	X	XX
$g^{(2)} (0)$	0.017(4)	0.011(3)	0.020(3)	0.034(4)
Lifetime (ps)	238(3)	116(2)	252(9)	72(3)
Pair generation efficiency	0.91(2)	0.87(2)
FSS ( $μ eV$ )	1.13(7)	0.96(9)
Calculated concurrencea	0.905	0.900
Measured concurrence	0.904(3)	0.713(8)
Calculated fidelity to $\| ϕ^{+} ⟩$ a	0.959	0.960
Measured fidelity to $\| ϕ^{+} ⟩$	0.975(1)	0.925(2)

Table 1. Summarized emitter performance for two representative QDs in a diode structure excited by TPE, measured at temperatures of 5 K and 20 K, respectively.