Teleportation systems toward a quantum internet
Quantum teleportation is essential for many quantum information technologies, including long-distance quantum networks. Using fiber-coupled devices, including state-of-the-art low-noise superconducting nanowire single-photon detectors and off-the-shelf optics, we achieve conditional quantum teleportation of time-bin qubits at the telecommunication wavelength of 1536.5 nm. We measure teleportation fidelities of ≥9% that are consistent with an analytical model of our system, which includes realistic imperfections. To demonstrate the compatibility of our setup with deployed quantum networks, we teleport qubits over 22 km of single-mode fiber while transmitting qubits over an additional 22 km of fiber. Our systems, which are compatible with emerging solid-state quantum devices, provide a realistic foundation for a high-fidelity quantum Internet with practical devices.
1. A quantum teleportation system, comprising:
a transmitter generating first photons;
a source of pairs of entangled photons, each pair comprising a second photon entangled with a third photon;
a coupler electromagnetically coupled to the transmitter and the source of pairs of entangled photons;
a pair of detectors D1 and D2 electromagnetically coupled to the coupler;
a receiver including a detection system comprising a detector D3 detecting the third photons;
an optical fiber connecting the detector D3 and the source of pairs of entangled photons, wherein the detector D3 detects the third photons transmitted along the optical fiber;
a clock distribution system outputting one or more clock signals controlling timing of the first photons, the second photons, and the third photons such that:
the coupler interacts one of the first photons, carrying a first qubit, and one of the second photons, carrying a second qubit, to form an interference;
the pair of detectors D1 and D2 detect the interference used to obtain a Bell State Measurement of a quantum system comprising the first qubit and the second qubit;
the detector D3 detects one of the third photons entangled with the one of the second photons and outputs a signal in response thereto; and
the detection system reads a state of the first qubit using the signal and the Bell State Measurement;
a data acquisition system acquiring arrival times of the first photons and the second photons at the detectors D1 and D2, and the arrival times of the third photons at the detector D3, wherein the arrival times are tagged with reference to the clock signals; and
a computer benchmarking the quantum teleportation system in real time using the arrival times, wherein the benchmarking comprises using a model simulating at least one of teleportation fidelity of the first qubit teleported to the one of the third photons received at the detector D3, or a degree of indistinguishability between the one of the first photons and the one of the second photons, as a function of a mean number of the second photons, wherein the model is calibrated and validated using measurements of the teleportation fidelity and the degree of indistinguishability.
2. The system of claim 1 , wherein:
the transmitter generates pulses of electromagnetic radiation each comprising one or more of the first photons,
the system further comprises:
a first attenuator attenuating the pulses of electromagnetic radiation so as to output attenuated pulses each comprising a first mean number of the first photons, the first mean number of the first photons received on the coupler increasing a likelihood the coupler interacts a single one of the first photons with a single one of the second photons to form the interference;
a first filter electromagnetically coupled to the coupler and spectrally filtering the electromagnetic radiation so as to increase indistinguishability between the one of the first photons and the one of the second photons;
one or more second filters electromagnetically coupled to the source of pairs of entangled photons and spectrally filtering the entangled photons;
the first qubit and the second qubit each comprise a time bin qubit comprising a superposition of an early photon with a later arriving photon; and
the source of entangled photons comprises a laser pumping a nonlinear material so as to output the second photons comprising idler photons and the third photons comprising signal photons according to a spontaneous parametric down conversion (SPDC) process.
3. The system of claim 2 , wherein the computer uses the benchmarking to output feedback used to optimize at least one of the timing, an intensity of the entangled photons outputted from the source of entangled photons, the spectral filtering of the photons, or an amount of attenuation of the pulses of electromagnetic radiation, so as to achieve the teleportation fidelity greater than 0.90 when the third photons travel a distance of at least 22 kilometers along the optical fiber.
4. The system of claim 1 , wherein the benchmarking comprises determining at least one of the teleportation fidelity of the first qubit teleported to the one of the third photons received at D3, the degree of indistinguishability between the one of the first photons and the one of the second photons, or a threefold coincidence photon detection rate of one of the photons being coincidentally detected at each of D1, D2, and D2.
5. The system of claim 1 , wherein the coupler comprises a beamsplitter or a linear optical device capable of interfering photons or electromagnetic fields.
6. The system of claim 5 , wherein the model calculates a probability of the detectors D1, D2, and D3 receiving one of the first photons, one of the second photons and one of the third photons in a same clock cycle, using a fitting parameter comprising a transmittance representing the amount of indistinguishability.
7. The system of claim 1 , wherein:
the first qubit and the second qubit each comprise a time bin qubit comprising a superposition of an early photon with a later arriving photon;
the source of entangled photons comprises a laser pumping a nonlinear material so as to output the one of the second photons comprising an idler photon and the one of the third photons comprising a signal photon according to a spontaneous parametric down conversion (SPDC) process;
the clock signals comprise clock cycles;
the data acquisition system measures the mean number of the second photons by comparing:
a coincidence rate, comprising events wherein the one of the second photons and
the one of the third photons in the one of the pairs of entangled photons are detected in a same one of the clock cycles; and
an accidental rate, comprising events wherein the one of the second photons and
the one of the third photons in the one of the pairs of entangled photons are detected in different clock cycles,
the degree of indistinguishability is measured by performing a Hong-Ou-Mandel experiment observing the interference using the coupler comprising a beamsplitter; and
the teleportation fidelity is measured using an interferometer measuring visibility of interference of the third photon with itself.
8. The system of claim 7 , wherein the model computes the teleportation fidelity and the degree of indistinguishability by:
determining a probability P 3f of a threefold coincidence detection of one of the photons on each of the detectors D1, D2 and D3:
P
3
f
=
Tr
{
ρ
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where:
â and {circumflex over (b)} operators represent modes of the one of the first photons and the one of the second photons, respectively, that are indistinguishable,
ĉ represents a mode of the one of the third photons directed on the detector D 3 , and
ρ AB =(|α α|)⊗(|Ψ TMSV Ψ TMSV |) represents a quantum state of the quantum system;
determining the amount of indistinguishability V HOM (ζ)=[P 3f (0)−P 3f (ζ)]/P 3f (0)
where ζ is an amount of indistinguishability between the first qubit and the second qubit, such that ζ=1 (ζ=0) corresponds to a case when both the first qubit and the second qubit are perfectly indistinguishable (distinguishable); and
determining the teleportation fidelity F(ζ)=P 3f (ζ,φ max )/[P 3f (ζ,φ max )+P 3f (ζ,φ min )], where φ max (φ min ) is a maximum (minimum) phase added into a path of the one of the second photons, corresponding to a maximum (minimum) rate of the threefold coincidence detection.
9. The system of claim 8 , wherein:
1.
P
3
f
(
ζ
)
=
1
-
2
exp
(
-
(
μ
A
/
2
)
[
1
+
(
1
-
ζ
2
)
η
i
μ
B
/
2
]
1
+
η
i
μ
B
/
2
)
1
+
η
i
μ
B
/
2
-
1
1
+
η
3
μ
B
+
exp
(
-
μ
A
)
1
+
η
i
μ
B
-
exp
(
-
μ
A
)
1
+
(
1
-
η
3
)
η
i
μ
B
+
η
3
μ
B
+
2
exp
(
-
(
μ
A
/
2
)
[
1
+
(
1
-
ζ
2
)
(
1
-
η
3
)
η
i
μ
B
/
2
+
η
3
μ
B
]
1
+
(
1
-
η
3
)
η
i
μ
B
/
2
+
η
3
μ
B
)
1
+
(
1
-
η
3
)
η
i
μ
B
/
2
+
η
3
μ
B
where η i and η s are the transmission efficiencies of the second photons and the third photons, respectively, including the detector efficiencies, μ A is the mean number of the first photons per time bin, and μ B is the mean number of second photons per time bin.
10. The system of claim 9 , wherein:
the first qubit comprises a first time bin qubit and the second qubit comprises a second time bin qubit,
the clock signal comprises clock cycles;
the data acquisition system acquires:
a coincidence rate, comprising events wherein the one of the second photons and
the one of the third photons in the one of the pairs of entangled photons are detected in a same one of the clock cycles;
an accidental rate, comprising events wherein the one of the second photons and
the one of the third photons in the one of the pairs of entangled photons are detected in different ones of the clock cycles;
a first detection rate of the second photons; and
a second detection rate of the third photons;
η i is the second detection rate divided by the coincidence rate and η s is the first detection rate divided by the coincidence rate; and
the mean number of the second photons per time bin is the accidental rate divided by the coincidence rate.
11. The system of claim 1 , further comprising a display displaying the benchmarking.
12. A method of teleporting using a quantum teleportation system, comprising:
teleporting a first qubit, comprising:
performing a Bell State Measurement of a quantum system, comprising interfering one or more first photons, carrying the first qubit, and one or more second photons, carrying a second qubit, wherein the quantum system comprises one of the first photons and one of the second photons;
detecting one or more third photons, each of the third photons entangled with one of the second photons prior to the interfering;
reading a state of the first qubit using the Bell State Measurement;
acquiring arrival times of the first photons and the second photons at detectors D1, D2 used to perform the Bell State Measurement, and the arrival times of the third photons at the receiver, wherein the arrival times are tagged with reference to clock signals; and
benchmarking the quantum teleportation system in real time using the arrival times.
13. The method of claim 12 , wherein the benchmarking comprises using a model simulating at least one of teleportation fidelity of the first qubit teleported to the one of the third photons received at the detector D3, or the degree of indistinguishability between the one of the first photons and the one of the second photons, as a function of a mean number of the second photons, wherein the model is calibrated and validated using measurements of the teleportation fidelity and the degree of indistinguishability.
14. A computer implemented system, comprising:
one or more processors; one or more memories; and an application stored in the one or more memories, the application executed by the one or more processors:
benchmarking a quantum teleportation system in real time, the quantum teleportation system:
teleporting a first qubit, comprising:
performing a Bell State Measurement of a quantum system, comprising
interfering one or more first photons, carrying the first qubit, and one or more second photons, carrying a second qubit, wherein the quantum system comprises one of the first photons and one of the second photons;
detecting one or more third photons at a receiver, each of the third photons entangled with one of the second photons prior to the interfering;
reading a state of the first qubit using the Bell State Measurement; wherein:
the benchmarking comprises the application:
receiving arrival times of the first photons and the second photons at detectors D1, D2 used to perform the Bell State Measurement, and the arrival times of the third photons at the receiver, wherein the arrival times are tagged with reference to clock signals; and
using the arrival times to determine at least one of a teleportation fidelity of the first qubit teleported to the one of the third photons received at D3, a degree of indistinguishability between the one of the first photons and the one of the second photons, or a threefold coincidence photon detection rate of one of the photons being coincidentally detected at each of D1, D2, and D2.
15. The system of claim 14 , further comprising:
a transmitter generating pulses of electromagnetic radiation each comprising one or more of the first photons,
a first attenuator attenuating the pulses of electromagnetic radiation so as to output attenuated pulses each comprising a first mean number of the first photons, the first mean number of photons received on a coupler increasing a likelihood the coupler interacts a single one of the first photons with a single one of the second photons to form an interference;
a first filter electromagnetically coupled to the coupler and spectrally filtering the electromagnetic radiation so as to increase indistinguishability between the one of the first photons and the one of the second photons;
one or more second filters electromagnetically coupled to a source of pairs of entangled photons (comprising one of the second photons and one of the third photons) and spectrally filtering the entangled photons;
the first qubit and the second qubit each comprise a time bin qubit comprising a superposition of an early photon with a later arriving photon; and
the source of the pairs of the entangled photons comprises a laser pumping a nonlinear material so as to output the second photons comprising idler photons and the third photons comprising signal photons according to a spontaneous parametric down conversion (SPDC) process.
16. The system of claim 15 , wherein the coupler comprises a beamsplitter or a linear optical device capable of interfering photons or electromagnetic fields.
17. The system of claim 15 , wherein:
the clock signal comprises clock cycles;
a data acquisition system measures a mean number of the second photons by comparing:
a coincidence rate, comprising events wherein the one of the second photons and
the one of the third photons in the pair of entangled photons are detected in a same one of the clock cycles; and
an accidental rate, comprising events wherein the one of the second photons and
the one of the third photons in the entangled pair are detected in different clock cycles,
the degree of indistinguishability is measured by performing a Hong-Ou-Mandel experiment observing the interference using the coupler comprising a beamsplitter; and
the teleportation fidelity is measured using an interferometer measuring visibility of interference of the third photon with itself.
18. The system of claim 14 , wherein the benchmarking comprises using a model simulating at least one of teleportation fidelity of the first qubit teleported to the one of the third photons received at the detector D3, or the degree of indistinguishability between the one of the first photons and the one of the second photons, as a function of a mean number of the second photons, wherein the model is calibrated and validated using measurements of the teleportation fidelity and the degree of indistinguishability.
19. The system of claim 18 , wherein the model computes the teleportation fidelity and the amount of indistinguishability by:
determining a probability P 3f of a threefold coincidence detection of one of the photons on each of the detectors D1, D2 and D3:
P
3
f
=
Tr
{
ρ
AB
(
𝕀
-
(
❘
"\[LeftBracketingBar]"
0
〉
〈
0
❘
"\[RightBracketingBar]"
)
a
^
1
,
a
^
2
,
a
^
3
⊗
3
)
⊗
(
𝕀
-
(
❘
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0
〉
〈
0
)
b
^
1
,
b
^
2
,
b
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0
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)
c
^
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}
where:
â and {circumflex over (b)} operators represent modes of the one of the first photons and the one of the second photons, respectively, that are indistinguishable,
ĉ represents a mode of the one of the third photons directed on the detector D 3 , and
ρ AB =(|α α|)⊗(|Ψ TMSV Ψ TMSV |) represents a quantum state of the quantum system;
determining the amount of indistinguishability V HOM (ζ)=[P 3f (0)−P 3f (ζ)]/P 3f (0)
where ζ is an amount of indistinguishability between the first qubit and the second qubit, such that ζ=1(ζ=0) corresponds to the case when both the first qubit and the second qubit are perfectly indistinguishable (distinguishable); and
determining the teleportation fidelity F(ζ)=P 3f (ζ,φ max )/[P 3f (ζ,φ max )+P 3f (ζ,φ min )], where φ max (φ min ) is a maximum (minimum) phase added into a path of the one of the second photons, corresponding to a maximum (minimum) rate of the threefold coincidence detection.
20. The system of claim 19 , wherein:
P
3
f
(
ζ
)
=
1
-
2
exp
(
-
(
μ
A
/
2
)
[
1
+
(
1
-
ζ
2
)
η
i
μ
B
/
2
]
1
+
η
i
μ
B
/
2
)
1
+
η
i
μ
B
/
2
-
1
1
+
η
3
μ
B
+
exp
(
-
μ
A
)
1
+
η
i
μ
B
-
exp
(
-
μ
A
)
1
+
(
1
-
η
3
)
η
i
μ
B
+
η
3
μ
B
+
2
exp
(
-
(
μ
A
/
2
)
[
1
+
(
1
-
ζ
2
)
(
1
-
η
3
)
η
i
μ
B
/
2
+
η
3
μ
B
]
1
+
(
1
-
η
3
)
η
i
μ
B
/
2
+
η
3
μ
B
)
1
+
(
1
-
η
3
)
η
i
μ
B
/
2
+
η
3
μ
B
where η i and η s are the transmission efficiencies of the second photons and the third photons, respectively, including the detector efficiencies, μ A is the mean number of the first photons per time bin, and μ B is the mean number of second photons per time bin.