OPTICAL NETWORKING OF SUPERCONDUCTING QUANTUM NODES

WITH TRANSDUCTION DEVICES

1. ABSTRACT

7. FUTURE RESEARCH TOPICS

1COMMUNICATIONS TECHNOLOGY LABORATORY, NIST, BOULDER, CO; 2PHYSICS DEPARTMENT, UNIVERSITY OF COLORADO, BOULDER, CO

TASSHI DENNIS

1

, AKIRA KYLE

2

, CURTIS RAU

2

• For superconducting quantum computers to continue to scale, 

multiple processors will need to be networked.

• Optical channels provide a low-loss link capable of spanning 

long distances.

• Combining hot optical photons with milliKelvin

superconducting circuits at microwave frequencies in a 

dilution refrigerator would appear incompatible.

Question 1: How do we connect the microwave and optical 

regimes quantum mechanically?

Question 2: What is the best way to use optical channels to 

entangle superconducting processor nodes?

Question 3: Will YOU be the first person in the world to 

experimentally demonstrate a “Quantum Internet” capable of 

distributing arbitrary quantum states?

2. MICROWAVE-OPTICAL TRANSDUCTION

• Demonstration of extrinsic optical distribution through transducers.

• Demonstration of short-distance entanglement of superconducting nodes.

• Demonstration of long-distance entanglement of superconducting nodes.

• Demonstration of entanglement across a free-space channel.

• Heterogenous quantum network demonstration between superconducting 

qubits and trapped ion nodes.

• Networking with exotic optical states with non-Gaussian processes.

• Networking with distillation of weak Gaussian states or coherent 

feedback control to overcome noise and loss.

6. EXPERIMENTALLY MAKING IT WORK

Collaborators at CU/JILA: Lehnert/Regal Lab 5. NETWORK TOPOLOGY STUDY

• Three coupled resonators (optical, mechanical, microwave): with 

“membrane in the middle”

3. CONTINUOUS VARIABLES APPROACH

• Based on measuring continuous field quadratures instead of discrete 

number states. This is an infinite Hilbert Space ==> It’s Analog!

• Practical preparation, manipulation, measurement of states. Protocols 

for teleportation and distillation known and feasible. Higher information 

capacity than discrete variables (DV). Can distill to DV if needed.

• Optics: A quantized electromagnetic field ==> use squeezed light.

4. SQUEEZED LIGHT

Contact: tasshi@nist.gov

Bidirectional and Efficient Conversion Between Microwave and Optical Light, R. W. Andrews, R. W. Peterson, T. 

P. Purdy, K. Cicak, R. W. Simmonds, C. A. Regal, and K. W. Lehnert, Nature Physics 10, 321-326, 2014.

Harnessing Electro-Optic Correlations in an Efficient Mechanical Converter, A. P. Higginbotham, P. S. Burns, M. 

D. Urmey, R. W. Peterson, N. S. Kampel, B. M. Brubaker, G. Smith, K. W. Lehnert, and C. A. Regal, Nature 

Physics 14, 1038-1042, 2018.

vibrating membrane 

superconducting circuit 

optical cavity 

Efficiency: 47% (record)

Added noise: 9 photons

Target < 1 photon

C L

To Fiber

To Qubit

Optical Port Microwave Port

• Bidirectional

• Can generate 

microwave-optical 

squeezing

Collaborators at NIST: Silverman/Mirin Lab

• Three coupled resonators (optical, acoustic, microwave): with 

quantum dot emitter

• High generation rates

• Integrated design

• Low power

Optical Quadratures:

∆E1

2 ∆E22 ≥ 1/4

Uncertainty Principle :

The proportion is not fixed.

Unequal is “squeezed.”

Entanglement from Two Mode Squeezing:

Entangled Pair of EPR Beams CV Quant. Networking Resource

For imperfect transducers, lossy channel, Gaussian operations, is it better to:

• Distribute or swap entanglement?

• Squeeze in the optical, microwave, or combined optical/microwave 

domain?

• Introduce squeezing intrinsic or extrinsic to transducers?

Optical Paths

Electrical Paths

Distribute: Swap:

Modeling the Network Topologies:

Y1 quadrature noise is below 

vacuum fluctuations; Y2 is above.

Precision metrology: LIGO

Transducer Hamiltonian of coupled resonators

• Transducer cooperativities, 

transmissivities, thermal 

noise (Temp. > 0).

• Optical channel Loss.

• Calculate entanglement 

thresholds.

Solid: distribution

Dash: swap

Extrinsic Optical

Intrinsic Optical

Intrinsic Micro.

Thermal Noise

Trans. Efficiency Transmission

• Extrinsic Optical Distribution is best choice for (realistic!) high loss.

Squeezed source

BS

Squeezed source

Alice

Bob

var E1a − E1b

2

< 1/2

var E2a + E2b

2

< 1/2

Entangled 

Quad.

Entangled 

Quad.

PPL LiNbO2 

~

PDH Lock 

1064 nm NPRO ISO 

Ref Cavity

EOM FR EOM PZT 

~

ISO 

Resonant Doubling Cavity

Laser Source

PPL LiNbO2 

Optical Parametric Amplifier

Entangled Light Source

Entangled

TMSV

Transducer

532 nm

1064 nm

532 nm

Homodyne

State 

Tomography

Entanglement 

Verification

1060 nm Laser, 2W, 

1 kHz linewidth

NIST Dilution 

Refrigerator

CU/JILA Dilution 

Refrigerator

Dilution Refrigerator

532 nm Green Light

Reference Cavity

Homodyne 

Detection

Two-Mode Squeeze 

Light Source

Resonant Doubling Cavity

Cavity Qubit Cavity Qubit

15 Servo Loops

Fiber Link Fiber Link