CRYOGENIC DRAM BASED MEMORY SYSTEM FOR SCALABLE QUANTUM COMPUTERS: A FEASIBILITY STUDY

Transcription

1 CRYOGENIC DRAM BASED MEMORY SYSTEM FOR SCALABLE QUANTUM COMPUTERS: A FEASIBILITY STUDY MEMSYS-2017 SWAMIT TANNU DOUG CARMEAN MOINUDDIN QURESHI

2 Why Quantum Computers? 2 Molecule and Material Simulations Quantum computers provide large speedup for problems in material science, machine learning, and medicine Execution Time Billion Years Days Classical Computer Quantum Computer Problem Size Quantum Computers enable solutions to important problems

3 3 Qubits: Background State of a Classical Bit 1 or 0 two points on sphere Classical Bit Quantum computer use quantum bits (qubits) to encode the information

4 3 Qubits: Background State of a Classical Bit 1 or 0 two points on sphere Quantum Classical Bit Quantum computer use quantum bits (qubits) to encode the information

5 3 Qubits: Background State of a Classical Bit 1 or 0 two points on sphere Quantum Classical Bit State of a Quantum Bit Any point on the sphere Quantum computer use quantum bits (qubits) to encode the information

6 4 Organization of Quantum Computer Control Processor Qubits Quantum Computer

7 4 Organization of Quantum Computer Control Processor Qubits Quantum Computer

8 4 Organization of Quantum Computer Control Processor Qubits Quantum Computer

9 4 Organization of Quantum Computer Control Processor Qubits Quantum Computer Control Processor --Interface between Qubits & Programmer

10 5 Qubits are fickle No quantization small change in state lead to errors 1 Room temperature too noisy to operate 0 Classical Bit Quantum Bit Qubits are kept at extremely low temperature (~20mK)

11 5 Qubits are fickle No quantization small change in state lead to errors 1 Room temperature too noisy to operate 0 Classical Bit Quantum Bit Qubits are kept at extremely low temperature (~20mK)

12 5 Qubits are fickle No quantization small change in state lead to errors 1 Room temperature too noisy to operate 0 Classical Bit Quantum Bit Qubits are kept at extremely low temperature (~20mK)

13 Todays Quantum Computer Dilution Refrigerator 5 Qubit Chip (IBM) 20mK

14 Todays Quantum Computer Dilution Refrigerator 5 Qubit Chip (IBM) Qubits 20mK 5 Qubit Chip (IBM)

15 Cryogenic Control Processor 7 Control Processor 300K Qubits 20mK

16 Cryogenic Control Processor 7 Control Processor 300K Qubits 20mK

17 Cryogenic Control Processor 7 Control Processor 300K Large Thermal Gradient Metal Wires Thermal Leakage Qubits 20mK

18 Cryogenic Control Processor 7 Control Processor 300K Large Thermal Gradient Metal Wires Thermal Leakage Qubits 20mK

19 Cryogenic Control Processor 7 Control Processor 300K Control Processor 4K Large Thermal Gradient Metal Wires Thermal Leakage Qubits 20mK Qubits 20mK

20 Cryogenic Control Processor 7 Control Processor 300K Control Processor 4K Large Thermal Gradient Metal Wires Thermal Leakage Superconducting wires Low Leakage Qubits 20mK Qubits 20mK

21 Cryogenic Control Processor is essential for scalable Quantum Computer (Ref: D. Carmean, ISCA 16 Keynote) Cryogenic Control Processor 7 Control Processor 300K Control Processor 4K Large Thermal Gradient Metal Wires Thermal Leakage Superconducting wires Low Leakage Qubits 20mK Qubits 20mK

22 8 Memory for Quantum Computers Memory Control Processor Qubits Program Memory + Data Memory Stores Quantum Executable, Data, ECC-frames (~10s GB) Memory must be kept at cryo temperature to avoid large thermal gradient Josephson Junction technology works at 4K Limited memory density (only few Mb) Quantum Computer

23 8 Memory for Quantum Computers Memory Control Processor Qubits Program Memory + Data Memory Stores Quantum Executable, Data, ECC-frames (~10s GB) Memory must be kept at cryo temperature to avoid large thermal gradient Josephson Junction technology works at 4K Limited memory density (only few Mb) Quantum Computer

24 8 Memory for Quantum Computers Program Memory Data Memory Memory Control Processor Qubits Program Memory + Data Memory Stores Quantum Executable, Data, ECC-frames (~10s GB) Memory must be kept at cryo temperature to avoid large thermal gradient Josephson Junction technology works at 4K Limited memory density (only few Mb) Quantum Computer

25 8 Memory for Quantum Computers Program Memory Data Memory Memory Control Processor Qubits Program Memory + Data Memory Stores Quantum Executable, Data, ECC-frames (~10s GB) Memory must be kept at cryo temperature to avoid large thermal gradient Josephson Junction technology works at 4K Limited memory density (only few Mb) Quantum Computer Quantum computers require substantial memory capacity at cryo temperature

26 9 Does commodity DRAM work at cryogenic temperatures?

27 9 Does commodity DRAM work at cryogenic temperatures? Goal: To characterize DRAM at cryogenic temperature to understand the functionality and error patterns

28 10 Why Memory Fails at Cryogenic Temperature? Temperature

29 10 Why Memory Fails at Cryogenic Temperature? Temperature Carriers (e - )

30 10 Why Memory Fails at Cryogenic Temperature? Temperature Carriers (e - )

31 10 Why Memory Fails at Cryogenic Temperature? Temperature Carriers (e - ) Threshold Voltage

32 10 Why Memory Fails at Cryogenic Temperature? Temperature Carriers (e - ) Threshold Voltage Faults

33 10 Why Memory Fails at Cryogenic Temperature? Temperature Carriers (e - ) Threshold Voltage Faults At low temperatures, carrier freezeout can cause increase in threshold voltage worsens error rate

34 10 Why Memory Fails at Cryogenic Temperature? Temperature Carriers (e - ) Threshold Voltage Faults Minimum Operational Temperature (MOT) Minimum temperature for fault free operation At low temperatures, carrier freezeout can cause increase in threshold voltage worsens error rate

35 EXECUTIVE SUMMARY 11 Why Cryogenic DRAM? Experimental Setup & Challenges Observations

36 12 How to Test DRAM at Cryogenic Temperature? Conventional memory testing Memtest86 running on host, dedicated memory testers

37 12 How to Test DRAM at Cryogenic Temperature? Conventional memory testing Memtest86 running on host, dedicated memory testers Host machines or memory testers do not work at cryogenic temperatures

38 12 How to Test DRAM at Cryogenic Temperature? Conventional memory testing Memtest86 running on host, dedicated memory testers Host machines or memory testers do not work at cryogenic temperatures Need mechanism to reduce DIMM temperature without affecting tester

39 13 Isolated Cooling of DIMM Need cryogenic coolant Liquid Nitrogen (boils at 77K) Need isolated cooling of DIMMs Compact cryogenic heatsink

40 13 Isolated Cooling of DIMM Need cryogenic coolant Liquid Nitrogen (boils at 77K) Need isolated cooling of DIMMs Compact cryogenic heatsink

41 13 Isolated Cooling of DIMM Need cryogenic coolant Liquid Nitrogen (boils at 77K) Need isolated cooling of DIMMs Compact cryogenic heatsink DIMM is sandwiched between two heatsinks and can be cooled down to 80K

42 13 Isolated Cooling of DIMM Need cryogenic coolant Liquid Nitrogen (boils at 77K) Need isolated cooling of DIMMs Compact cryogenic heatsink DIMM is sandwiched between two heatsinks and can be cooled down to 80K Compact heatsink with Liquid Nitrogen provides isolated cooling of a DIMM

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45 15 Challenges: Thermal Shock & Ice Condensation 300K Temperature (K) 80K Time Limit rate of cooling & use isolation chamber to reduce condensation

46 15 Challenges: Thermal Shock & Ice Condensation THERMAL SHOCK 300K Temperature (K) 80K Time Limit rate of cooling & use isolation chamber to reduce condensation

47 15 Challenges: Thermal Shock & Ice Condensation THERMAL SHOCK 300K Temperature (K) 80K Time Limit rate of cooling & use isolation chamber to reduce condensation

48 15 Challenges: Thermal Shock & Ice Condensation THERMAL SHOCK Temperature (K) 300K 80K Condensation Time Limit rate of cooling & use isolation chamber to reduce condensation

49 15 Challenges: Thermal Shock & Ice Condensation THERMAL SHOCK Temperature (K) 300K 80K Condensation Time Limit rate of cooling & use isolation chamber to reduce condensation

50 15 Challenges: Thermal Shock & Ice Condensation THERMAL SHOCK Temperature (K) 300K 80K Condensation Time Limit rate of cooling & use isolation chamber to reduce condensation

51 Experimental Methodology 16 Number of DIMMS 55 Verify memory functionality by using march-tests Number of Chips 750 Fault single bit fault in a burst Number of Vendors 5 MOT Minimum temperature at which no faults are observed

52 17 Minimum Operational Temperature for DIMMs Minimum Operating Temperature (K) % 90% 55% 18% % DIMMs are functional below 90K

53 17 Minimum Operational Temperature for DIMMs Minimum Operating Temperature (K) DIMM Failure! 100% 90% 55% 18% % DIMMs are functional below 90K

54 18 Chip Failures 8% Functional Chips 92% Faulty Chip 92% of chips worked at cryogenic conditions Pick cryogenic tolerant chips

55 Min Operational Temperature Vs Chip Capacity Mb 512 Mb 1 Gb 2 Gb 4 Gb Minimum Operating Temperature (K) MOT increases with capacity; capacity of chip is correlated to technology node

56 Min Operational Temperature Vs Chip Capacity Mb 512 Mb 1 Gb 2 Gb 4 Gb Minimum Operating Temperature (K) MOT increases with capacity; capacity of chip is correlated to technology node

57 20 Fault Granularity Single bit errors Uncorrelated faults Single bit fault % Linear codes (SECDED, BCH) are still effective Double bit fault 0.015% Uncorrelated faults Conventional ECC can be effective for Cryo DRAM

58 21 Transient Vs Permanent Faults Repeated faulty addresses = permanent error Unique faulty address = transient error DDR2 DDR3 DDR4 Permanent 64% Transient 36% Permanent 59% Transient 41% Permanen t 47% Transient 53% Permanent faults conventional sparing techniques can be used

59 22 Conclusion Quantum computers need dense memory at low temperature Does DRAM Work at cryogenic temperature? Experiments show most commodity DRAM chips work at 90K Error patterns are amenable to existing fault tolerance techniques

60 23 Questions?

61 23 Questions? Want to know more about quantum computers?

62 23 Questions? Want to know more about quantum computers? Please visit my paper presentation at MICRO 2017 In 2 weeks in Boston!

63 24 Backup slides

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66 28 Most Chips Work at 80K 7% Faulty Chips per DIMM 92% Functional Chips One Faulty Chip Two Faulty Chips Three Faulty Chips Four Faulty Chips Only 8% of chips fail at 80K Pick cryo tolerant chips